View Filing Data

Print Document View Excel Document

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2017	Feb. 23, 2018	Jun. 30, 2017
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	FY
Trading Symbol	ATRC
Entity Registrant Name	AtriCure, Inc.
Entity Central Index Key	0001323885
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Common Stock, Shares Outstanding		34,560,275
Entity Public Float			$ 797.2

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 21,809	$ 24,208
Short-term investments	12,642	19,801
Accounts receivable, less allowance for doubtful accounts of $32 and $246	23,083	21,094
Inventories	22,451	17,660
Other current assets	2,273	2,954
Total current assets	82,258	85,717
Property and equipment, net	28,749	29,995
Long-term investments		3,000
Intangible assets, net	50,764	52,131
Goodwill	105,257	105,257
Other noncurrent assets	676	321
Total Assets	267,704	276,421
Current liabilities:
Accounts payable	12,431	10,673
Accrued liabilities	18,911	16,467
Other current liabilities and current maturities of capital leases and long-term debt	561	1,688
Total current liabilities	31,903	28,828
Capital leases	12,761	13,319
Long-term debt	24,100	23,886
Other noncurrent liabilities	37,774	41,946
Total Liabilities	106,538	107,979
Commitments and contingencies (Note 10)
Stockholders' Equity:
Common stock, $0.001 par value, 90,000 shares authorized and 34,586 and 33,342 issued and outstanding	35	33
Additional paid-in capital	386,963	367,851
Accumulated other comprehensive income (loss)	34	(468)
Accumulated deficit	(225,866)	(198,974)
Total Stockholders' Equity	161,166	168,442
Total Liabilities and Stockholders' Equity	$ 267,704	$ 276,421

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Consolidated Balance Sheets [Abstract]
Accounts receivable, allowance for doubtful accounts	$ 32	$ 246
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	90,000,000	90,000,000
Common stock, shares issued	34,586,000	33,342,000
Common stock, shares outstanding	34,586,000	33,342,000

Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Consolidated Statements of Operations and Comprehensive Loss [Abstract]
Revenue	$ 174,716	$ 155,109	$ 129,755
Cost of revenue	48,553	44,008	36,880
Gross profit	126,163	111,101	92,875
Operating expenses:
Research and development expenses	34,144	35,824	25,742
Selling, general and administrative expenses	116,998	106,415	93,853
Total operating expenses	151,142	142,239	119,595
Loss from operations	(24,979)	(31,138)	(26,720)
Other income (expense):
Interest expense	(2,264)	(1,801)	(292)
Interest income	227	227	190
Other	138	(586)	(354)
Loss before income tax expense	(26,878)	(33,298)	(27,176)
Income tax expense	14	40	36
Net loss	$ (26,892)	$ (33,338)	$ (27,212)
Basic and diluted net loss per share	$ (0.83)	$ (1.05)	$ (0.97)
Weighted average shares outstanding — basic and diluted	32,387	31,609	28,058
Comprehensive loss:
Unrealized gain on investments	$ 15	$ 18	$ 15
Foreign currency translation adjustment	487	125	(278)
Other comprehensive income (loss)	502	143	(263)
Net loss	(26,892)	(33,338)	(27,212)
Comprehensive loss, net of tax	$ (26,390)	$ (33,195)	$ (27,475)

Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Total
Beginning Balance at Dec. 31, 2014	$ 28	$ 271,282	$ (138,424)	$ (348)	$ 132,538
Beginning Balance, Shares at Dec. 31, 2014	27,580
Issuance of common stock through public offering	$ 3	68,985			68,988
Issuance of common stock through public offering, Shares	3,757
Issuance of common stock under equity incentive plans	$ 1	1,920			1,921
Issuance of common stock under equity incentive plans, Shares	850
Issuance of common stock under employee stock purchase plan		1,539			1,539
Issuance of common stock under employee stock purchase plan, Shares	87
Reclassification of non-employee option liability		177			177
Share-based employee compensation expense		8,997			8,997
Other comprehensive loss				(263)	(263)
Net loss			(27,212)		(27,212)
Ending Balance at Dec. 31, 2015	$ 32	352,900	(165,636)	(611)	186,685
Ending Balance, Shares at Dec. 31, 2015	32,274
Issuance of common stock under equity incentive plans	$ 1	1,636			1,637
Issuance of common stock under equity incentive plans, Shares	934
Issuance of common stock under employee stock purchase plan		1,618			1,618
Issuance of common stock under employee stock purchase plan, Shares	134
Share-based employee compensation expense		11,697			11,697
Other comprehensive loss				143	143
Net loss			(33,338)		(33,338)
Ending Balance at Dec. 31, 2016	$ 33	367,851	(198,974)	(468)	168,442
Ending Balance, Shares at Dec. 31, 2016	33,342
Issuance of common stock under equity incentive plans	$ 2	2,387			2,389
Issuance of common stock under equity incentive plans, Shares	1,112
Issuance of common stock under employee stock purchase plan		2,110			2,110
Issuance of common stock under employee stock purchase plan, Shares	132
Share-based employee compensation expense		14,615			14,615
Other comprehensive loss				502	502
Net loss			(26,892)		(26,892)
Ending Balance at Dec. 31, 2017	$ 35	$ 386,963	$ (225,866)	$ 34	$ 161,166
Ending Balance, Shares at Dec. 31, 2017	34,586

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net loss	$ (26,892)	$ (33,338)	$ (27,212)
Adjustments to reconcile net loss to net cash used in operating activities:
Share-based compensation expense	14,615	11,697	8,997
Depreciation	7,761	7,655	4,975
Amortization of intangible assets	1,367	1,644	1,303
Amortization of deferred financing costs	264	218	61
Loss on disposal of property and equipment and impairment of assets	336	433	276
Realized gain (loss) from foreign exchange on intercompany transactions	(173)	407	434
Amortization/accretion on investments	30	126	577
Change in allowance for doubtful accounts	(172)	149	144
Change in fair value of contingent consideration	(4,078)	969
Changes in operating assets and liabilities, net of amounts acquired:
Accounts receivable	(1,464)	(1,982)	(900)
Inventories	(4,477)	(79)	(2,950)
Other current assets	829	122	(928)
Accounts payable	1,290	(1,072)	4,013
Accrued liabilities	2,228	(1,915)	3,070
Other noncurrent assets and liabilities	(408)	(153)	298
Net cash used in operating activities	(8,944)	(15,119)	(7,842)
Cash flows from investing activities:
Purchases of available-for-sale securities	(16,455)	(28,592)	(19,525)
Sales and maturities of available-for-sale securities	26,600	24,202	40,602
Purchases of property and equipment	(6,384)	(7,692)	(13,445)
Proceeds from sale of property and equipment		3
Increases in property under build-to-suit obligation			(10,552)
Cash paid for nContact business combination			(7,581)
Net cash provided by (used in) investing activities	3,761	(12,079)	(10,501)
Cash flows from financing activities:
Proceeds from debt borrowings		25,000
Payment on debt and capital leases	(1,689)	(439)	(263)
Proceeds from build-to-suit obligation			10,552
Proceeds from economic incentive loan			340
Payment of debt fees	(50)	(120)	(62)
Proceeds from stock option exercises	4,402	3,337	2,703
Shares repurchased for payment of taxes on stock awards	(2,013)	(1,701)	(782)
Proceeds from issuance of common stock under employee stock purchase plan	2,110	1,618	1,539
Payment of stock issuance fees			(66)
Net cash provided by financing activities	2,760	27,695	13,961
Effect of exchange rate changes on cash and cash equivalents	24	(53)	(238)
Net (decrease) increase in cash and cash equivalents	(2,399)	444	(4,620)
Cash and cash equivalents-beginning of period	24,208	23,764	28,384
Cash and cash equivalents-end of period	21,809	24,208	23,764
Supplemental cash flow information:
Cash paid for interest	2,002	1,506	232
Cash paid for income taxes	37	30	20
Non-cash investing and financing activities:
Accrued purchases of property and equipment	650	340	1,277
Assets acquired through capital lease	$ 2	152	50
Capital lease asset early termination		$ 37
Stock issuance in business combinations			69,054
Contingent consideration in business combinations			$ 40,207

Description of Business and Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2017

Description of Business and Summary of Significant Accounting Policies [Abstract]

Description of Business and Summary of Significant Accounting Policies

1. DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

Nature of the Business—The “Company” or “AtriCure” consists of AtriCure, Inc. and its wholly-owned subsidiaries. The Company is a leading innovator in treatments for atrial fibrillation (Afib) and left atrial appendage (LAA) management, and it sells its products to medical centers globally through its direct sales force and distributors.

Principles of Consolidation—The Consolidated Financial Statements include the accounts of the Company, AtriCure, LLC, Endoscopic Technologies, LLC and nContact Surgical, LLC, the Company’s wholly-owned subsidiaries, all organized in the State of Delaware; AtriCure Europe B.V. (AtriCure Europe), the Company’s wholly-owned subsidiary incorporated in the Netherlands; AtriCure Spain, S.L., AtriCure Europe’s wholly-owned subsidiary incorporated in Spain, AtriCure Germany GmbH, AtriCure Europe’s wholly-owned subsidiary incorporated in Germany, and AtriCure Hong Kong Limited, the Company’s wholly-owned subsidiary incorporated in Hong Kong. All intercompany accounts and transactions have been eliminated in consolidation.

Cash and Cash Equivalents—The Company considers highly liquid investments with maturities of three months or less at the date of acquisition as cash equivalents in the accompanying Consolidated Financial Statements.

Investments—The Company places its investments primarily in U.S. Government agencies and securities, corporate bonds and commercial paper and classifies all investments as available-for-sale. Investments with maturities of less than one year are classified as short-term investments. Investments are recorded at fair value, with unrealized gains and losses recorded as accumulated other comprehensive income (loss). Gains and losses are recognized using the specific identification method when securities are sold and are included in interest income or expense in the Consolidated Statements of Operations and Comprehensive Loss.

Revenue Recognition—The Company accounts for revenue in accordance with Financial Accounting Standards Board (FASB) Accounting Standards Codification (ASC) 605, “Revenue Recognition” (ASC 605). The Company recognizes revenue when all of the following criteria are met: (i) there is persuasive evidence that an arrangement exists, (ii) delivery of the products and/or services has occurred, (iii) the selling price is fixed or determinable, and (iv) collectability is reasonably assured.

Pursuant to the Company’s standard terms of sale, revenue is recognized when title to the goods and risk of loss transfers to customers and there are no remaining obligations that will affect the customers’ final acceptance of the sale. Generally, the Company’s standard terms of sale define the transfer of title and risk of loss to occur upon shipment to the respective customer. The Company does not maintain any post-shipping obligations to customers. No installation, calibration or testing of products is performed by the Company subsequent to shipment to the customer in order to render products operational.

Revenue includes shipping and handling revenue of $1,090, $1,266 and $1,056 in 2017, 2016 and 2015. Cost of freight for shipments to customers is included in cost of revenue. Sales and other value-added taxes collected from customers and remitted to governmental authorities are excluded from revenue. The Company sells its products primarily through a direct sales force, with sales made through distributors in select international markets. Terms of sale are generally consistent for both end-users and distributors except that payment terms are generally net 30 days for end-users and net 60 days for distributors, with limited exceptions.

Sales Returns and Allowances—The Company maintains a provision for sales returns and allowances to account for potential returns of defective or damaged products, products shipped in error and invoice adjustments, as well as current deferrals of revenue. The Company adjusts the provision quarterly using a combination of specific identification and an estimated general reserve based on historical experience. Increases to the provision result in a reduction of revenue. The provision is included in accrued liabilities in the Consolidated Balance Sheets.

Allowance for Doubtful Accounts Receivable—The Company evaluates the collectability of accounts receivable to determine the appropriate reserve for doubtful accounts. In determining the amount of the reserve, the Company considers aging of account balances, historical credit losses, customer-specific information and other relevant factors. An increase to the allowance for doubtful accounts results in a corresponding increase in selling, general and administrative expense. The Company reviews accounts receivable and adjusts the allowance based on current circumstances and charges off uncollectible receivables against the allowance when all attempts to collect the receivable have failed. The Company’s history of write-offs has not been significant.

Inventories—Inventories are stated at the lower of cost or net realizable value based on the first-in, first-out cost method (FIFO) and consist of raw materials, work in process and finished goods. The Company’s industry is characterized by rapid product development and frequent new product introductions. Uncertain timing of product approvals, variability in product launch strategies and variation in product use all impact inventory reserves for excess and obsolete products. An estimated inventory reserve for excess, slow moving and obsolete inventory is recorded quarterly. An increase to inventory reserves results in a corresponding increase in cost of revenue. Inventories are written off against the reserve when they are physically disposed.

Property and Equipment—Property and equipment is stated at cost less accumulated depreciation. Depreciation is computed using the straight-line method over the estimated useful lives of assets (see Note 7). The Company reassesses the useful lives of property and equipment annually and retires assets if they are no longer in service. Maintenance and repair costs are expensed as incurred.

The Company’s RF and cryo generators are generally placed with customers that use the Company’s disposable products. The estimated useful lives of this equipment are based on anticipated usage by customers and the timing and impact of expected new technology rollouts by the Company and may change in a future period if the Company experiences changes in the usage of the equipment or introduces new technologies. Depreciation related to generators and other capital equipment is recorded in cost of revenue in the Consolidated Statements of Operations and Comprehensive Loss.

The Company reviews property and equipment for impairment using its best estimates based on reasonable and supportable assumptions and projections of expected future cash flows. Property and equipment impairments recorded by the Company have not been significant.

Intangible Assets—Intangible assets with determinable useful lives are amortized on a straight-line basis over the estimated periods benefited (see Note 5).

Included in intangible assets is In Process Research and Development (IPR&D). The Company defines IPR&D as the value of acquired technology which has not yet reached technological feasibility. The primary basis for determining the technological feasibility is obtaining specific regulatory approvals. IPR&D is accounted for as an indefinite-lived intangible asset until completion or abandonment of the IPR&D project. Upon completion of the development project, the IPR&D will be amortized over its estimated useful life. If the IPR&D project is abandoned, the related IPR&D asset would be written off. The IPR&D asset represents an estimate of the fair value of the pre-market approval (PMA) that could result from the CONVERGE IDE clinical trial.

The Company reviews intangible assets for impairment using its best estimates based on reasonable and supportable assumptions and projections.

Goodwill—Goodwill represents the excess of purchase price over the fair value of the net assets acquired in business combinations. The Company tests goodwill for impairment annually on November 30, or more often if impairment indicators are present. The Company’s goodwill is accounted for in a single reporting unit representing the Company as a whole.

Other Noncurrent Liabilities—Other noncurrent liabilities consist of contingent consideration recorded in business combinations, deferred revenues and other contractual obligations. Although the Company expects to settle a portion of the contingent consideration liability within the following year, the balance is included in noncurrent liabilities as such settlement is both required and expected to be made in shares of the Company’s common stock pursuant to the nContact merger agreement.

Other Income (Expense)—Other income (expense) consists of foreign currency transaction gains and losses generated by settlements of intercompany balances denominated in Euros and invoices transacted in British Pounds.

Taxes— Deferred income tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases and operating loss and tax credit carryforwards. Deferred income tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred income tax assets and liabilities from a change in tax rates is recognized in the period that includes the enactment date.

The Company’s estimate of the valuation allowance for deferred income tax assets requires it to make significant estimates and judgments about its future operating results. Deferred income tax assets are reduced by valuation allowances if, based on the consideration of all available evidence, it is more-likely-than-not that some portion of the deferred income tax asset will not be realized. Significant weight is given to evidence that can be objectively verified. The Company evaluates deferred tax income assets on an annual basis to determine if valuation allowances are required by considering all available evidence. Deferred income tax assets are realized by having sufficient future taxable income to allow the related tax benefits to reduce taxes otherwise payable. The sources of taxable income that may be available to realize the benefit of deferred income tax assets are future reversals of existing taxable temporary differences, future taxable income, exclusive of reversing temporary differences and carryforwards, taxable income in carry-back years and tax planning strategies that are both prudent and feasible. In evaluating whether to record a valuation allowance, the applicable accounting standards deem that the existence of cumulative losses in recent years is significant objectively verifiable negative evidence that must be overcome by objectively verifiable positive evidence to avoid the need to record a valuation allowance. The Company has recorded a full valuation allowance against substantially all net deferred income tax assets as it is more-likely-than-not that the benefit of the deferred income tax assets will not be recognized in future periods.

A provision of The Patient Protection and Affordable Care Act enacted in 2010, as amended (PPACA), requires manufacturers of medical devices to pay an excise tax on all U.S. medical device sales. In December 2015, the U.S. government approved the suspension of the excise tax on medical device sales beginning January 1, 2016 through December 31, 2017. Then, in January 2018, the U.S. government approved an additional suspension of the excise tax on medical device sales from January 1, 2018 to December 31, 2019. The Company’s expense related to the medical device excise tax, which was recorded in cost of revenue, was $667 for the year ended December 31, 2015.

Net Loss Per Share—Basic and diluted net loss per share is computed in accordance with FASB ASC 260 “Earnings Per Share” (ASC 260) by dividing the net loss by the weighted average number of common shares outstanding during the period. Since the Company has experienced net losses for all periods presented, net loss per share excludes the effect of 4,321, 4,320 and 4,255 stock options and restricted stock shares as of December 31, 2017, 2016 and 2015 because they are anti-dilutive. Therefore, the number of shares calculated for basic net loss per share is also used for the diluted net loss per share calculation.

Comprehensive Income (Loss) and Accumulated Other Comprehensive Income (Loss)—In addition to net losses, the comprehensive loss includes foreign currency translation adjustments and unrealized gains and losses on investments.

Accumulated other comprehensive income (loss) consisted of the following (net of tax):



	2017		2016		2015
Total accumulated other comprehensive loss at beginning of period	$	(468)	$	(611)	$	(348)
Unrealized losses on investments
Balance at beginning of period	$	(21)	$	(39)	$	(54)
Other comprehensive income before reclassifications		15		18		15
Amounts reclassified from accumulated other comprehensive income (loss) to other income (loss)		—		—		—
Balance at end of period	$	(6)	$	(21)	$	(39)
Foreign currency translation adjustment
Balance at beginning of period	$	(447)	$	(572)	$	(294)
Other comprehensive income before reclassifications		660		532		156
Amounts reclassified from accumulated other comprehensive income (loss) to other income (loss)		(173)		(407)		(434)
Balance at end of period	$	40	$	(447)	$	(572)
Total accumulated other comprehensive income (loss) at end of period	$	34	$	(468)	$	(611)

Research and Development Costs— Research and development costs are expensed as incurred. These costs include compensation and other internal and external costs associated with the development of and research related to new and existing products or concepts, preclinical studies, clinical trials, healthcare compliance and regulatory affairs.

Advertising Costs— The Company expenses advertising costs as incurred. Advertising expense was $900, $625 and $476 during the years ended December 31, 2017, 2016 and 2015.

Share-Based Compensation—The Company follows FASB ASC 718 “Compensation-Stock Compensation” (ASC 718) to record share-based compensation for all share-based payment awards, including stock options, restricted stock and stock purchases related to an employee stock purchase plan, based on estimated fair values. The Company’s share-based compensation expense recognized under ASC 718 for the years ended December 31, 2017, 2016 and 2015 was $14,615, $11,697 and $8,997.

ASC 718 requires companies to estimate the fair value of share-based payment awards on the date of grant using an option-pricing model. The value of the portion of the award that is ultimately expected to vest is recognized as expense over the requisite service periods in the Company’s Consolidated Statements of Operations and Comprehensive Loss. The expense has been reduced for estimated forfeitures. The Company estimates forfeitures at the time of grant and revises them, if necessary, in subsequent periods if actual forfeitures differ from those estimates.

The Company estimates the fair value of time-based options on the date of grant using the Black-Scholes option-pricing model (Black-Scholes model). The Company’s determination of fair value is affected by the Company’s stock price, as well as assumptions regarding several subjective variables. These variables include, but are not limited to, the Company’s expected stock price volatility over the term of the awards and actual and projected employee stock option exercise behaviors. The fair value of market-based performance option grants is estimated at the date of grant using a Monte-Carlo simulation. The value of the portion of the awards that is ultimately expected to vest is recognized as expense over the requisite service periods in the Consolidated Statements of Operations and Comprehensive Loss.

The Company estimates the fair value of restricted stock based upon the grant date closing market price of the Company’s common stock.

The Company also has an employee stock purchase plan (ESPP) which is available to all eligible employees as defined by the plan document. Under the ESPP, shares of the Company’s common stock may be purchased at a discount. The Company estimates the number of shares to be purchased under the ESPP at the beginning of each purchase period based upon the fair value of the stock at the beginning of the purchase period using the Black-Scholes model and records estimated compensation expense during the period. Expense is adjusted at the time of stock purchase.

Use of Estimates—The preparation of the financial statements in conformity with accounting principles generally accepted in the United States of America (GAAP) requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenue and expense during the reporting period. Actual results could differ from those estimates.

Fair Value Disclosures— The Company classifies cash and investments in U.S. government agencies and securities as Level 1 within the fair value hierarchy. Accounts receivable, short-term other assets, accounts payable and accrued liabilities are also classified as Level 1. The carrying amounts of these assets and liabilities approximate their fair value due to their relatively short-term nature. Cash equivalents and investments in corporate bonds and commercial paper are classified as Level 2 within the fair value hierarchy. The fair value of fixed term debt is estimated by calculating the net present value of future debt payments at current market interest rates and is classified as Level 2. The book value of the Company’s fixed term debt approximates its fair value. Significant unobservable inputs with respect to the fair value measurement of the Level 3 contingent consideration liability are developed using Company data. When an input is changed, the corresponding valuation models are updated and the results are analyzed for reasonableness. See Note 3 – Fair Value for further information on fair value measurements.

Recent Accounting Pronouncements	12 Months Ended
Recent Accounting Pronouncements	Dec. 31, 2017
Recent Accounting Pronouncements [Abstract]
Recent Accounting Pronouncements	2. RECENT ACCOUNTING PRONOUNCEMENTS In May 2014 the FASB issued Accounting Standards Update (ASU) 2014-09, “Revenue from Contracts with Customers” (ASU 2014-09), which requires an entity to recognize revenue for the transfer of goods or services equal to the amount that it expects to be entitled in exchange for those goods or services. ASU 2014-09 supersedes most current revenue recognition guidance. In July 2015 the FASB deferred the effective date of ASU 2014-09 for entities reporting under U.S. GAAP from interim and annual reporting periods beginning after December 15, 2016 to interim and annual reporting periods beginning after December 15, 2017. A full retrospective or modified retrospective approach may be taken to adopt the guidance in the ASU. FASB ASU 2016-08, “Revenue from Contracts with Customers (Topic 606): Principal Versus Agent Considerations (Reporting Revenue Gross Versus Net)”, FASB ASU 2016-10, “Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing”, FASB ASU 2016-12, “Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients” and FASB ASU 2017-13, “Revenue Recognition (Topic 605), Revenue from Contracts with Customers (Topic 606), Leases (Topic 840), and Leases (Topic 842)” were issued to further refine the guidance in ASU 2014-09. The Company performed a comprehensive review of the requirements of ASU 2014-09. This review identified customer contracts and associated revenue streams within the scope of the new guidance by applying the five-step model of the new standard and comparing the results to current accounting to identify potential differences that would result from applying the requirements of the new standard. The Company’s revenue recognition related to product sales will remain substantially unchanged since the majority of the Company’s revenue arrangements consist of a single performance obligation related to the transfer of a promised good to a customer that allows the Company to recognize revenue at a point in time. The Company will adopt the new guidance as of January 1, 2018 using the modified retrospective adoption method. The adoption of ASU 2014-09 will not have a material impact on the amount and timing of revenue recognized in the consolidated financial statements. In February 2016 the FASB issued ASU 2016-02, “Leases” (ASU 2016-02) which requires lessees to record most leases onto their balance sheet but recognize expenses on their income statement in a manner similar to today’s accounting. The guidance is effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. Entities are required to use a modified retrospective approach for leases that exist or are entered into after the beginning of the earliest comparative period in the financial statements. Full retrospective application is prohibited. The Company is evaluating the provisions of ASU 2016-02 to determine the impact on its consolidated financial position, results of operations and related disclosures. In May 2017 the FASB issued ASU 2017-09, “Compensation — Stock Compensation (Topic 718), Scope of Modification Accounting” (ASU 2017-09), which amends the scope of modification accounting for share-based payment arrangements. ASU 2017-09 provides guidance on the types of changes to the terms or conditions of share-based payment awards to which an entity would be required to apply modification accounting under ASC 718. Specifically, an entity would not apply modification accounting if the fair value, vesting conditions, and classification of the awards are the same immediately before and after the modification. The new guidance also clarifies that a modification to an award could be significant and therefore require disclosure, even if modification accounting is not required. ASU 2017-09 is effective for annual reporting periods, including interim periods within those annual reporting periods, beginning after December 15, 2017. Early adoption is permitted, including adoption in any interim period. The Company will consider the new guidance in its accounting and financial reporting for modifications if and when they occur. In February 2018, the FASB issued ASU 2018-02, “Reclassification of Certain Tax Effects From Accumulated Other Comprehensive Income (AOCI)” (ASU 2018-02) to address industry concerns related to the application of ASC 740, “Income Taxes” to certain provisions of the new tax reform legislation. Upon adopting ASU 2018-02, an entity is required to disclose (1) its accounting policy related to releasing income tax effects from AOCI, (2) whether it has elected to reclassify, to retained earnings in the statement of stockholders’ equity, the stranded tax effects in AOCI related to the new tax reform legislation and (3) if it has elected to reclassify to retained earnings the stranded tax effects in AOCI related to the new tax reform legislation, what the reclassification encompasses. The guidance is effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. Early adoption is permitted. An entity will apply this guidance to each period in which the effect of the new tax reform legislation (or portion thereof) is recorded and may apply it either (1) retrospectively as of the date of enactment or (2) as of the beginning of the period of adoption. The Company is evaluating the provisions of ASU 2018-02 to determine the impact on its consolidated financial position, results of operations and related disclosures.

Fair Value

12 Months Ended

Dec. 31, 2017

Fair Value [Abstract]

Fair Value

3. FAIR VALUE

FASB ASC 820, “Fair Value Measurements and Disclosures” (ASC 820), defines fair value as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. The fair value hierarchy is based on three levels of inputs, of which the first two are considered observable and the last unobservable, that may be used to measure fair value:

Level 1—Quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date. An active market for the asset or liability is a market in which transactions for the asset or liability occur with sufficient frequency and volume to provide pricing information on an ongoing basis. The valuation under this approach does not entail a significant degree of judgment.

Level 2—Inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. The valuation technique for the Company’s Level 2 assets is based on quoted market prices for similar assets from observable pricing sources at the reporting date.

Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. Unobservable inputs shall be used to measure fair value to the extent that observable inputs are not available, thereby allowing for situations in which there is little, if any, market activity for the asset or liability at the measurement date.

The following table represents the Company’s fair value hierarchy for its financial assets and liabilities measured at fair value on a recurring basis as of December 31, 2017:



	Quoted Prices
	in Active		Significant		Significant
	Markets for		Other		Other
	Identical		Observable		Unobservable
	Assets		Inputs		Inputs
	(Level 1)		(Level 2)		(Level 3)		Total
Assets:
Money market funds	$	—	$	12,774	$	—	$	12,774
Commercial paper		—		7,472		—		7,472
U.S. government agencies and securities		2,999		—		—		2,999
Corporate bonds		—		2,920		—		2,920
Total assets	$	2,999	$	23,166	$	—	$	26,165
Liabilities:
Acquisition-related contingent consideration	$	—	$	—	$	37,098	$	37,098
Total liabilities	$	—	$	—	$	37,098	$	37,098

The following table represents the Company’s fair value hierarchy for its financial assets and liabilities measured at fair value on a recurring basis as of December 31, 2016:



	Quoted Prices
	in Active		Significant		Significant
	Markets for		Other		Other
	Identical		Observable		Unobservable
	Assets		Inputs		Inputs
	(Level 1)		(Level 2)		(Level 3)		Total
Assets:
Money market funds	$	—	$	17,085	$	—	$	17,085
Commercial paper		—		5,996		—		5,996
U.S. government agencies and securities		7,000		1,529		—		8,529
Corporate bonds		—		8,276		—		8,276
Total assets	$	7,000	$	32,886	$	—	$	39,886
Liabilities:
Acquisition-related contingent consideration	$	—	$	—	$	41,176	$	41,176
Total liabilities	$	—	$	—	$	41,176	$	41,176

There were no changes in the levels or methodology of measurement of financial assets and liabilities during the years ended December 31, 2017 and 2016.

Derivative Instruments. Vested non-employee options historically issued by the Company were accounted for as derivative liabilities and remeasured at fair value through earnings at each reporting period until exercised or forfeited. All vested non-employee options were exercised as of December 31, 2015.

The following table represents the Company’s Level 3 fair value measurements using significant other unobservable inputs for derivative instruments for each of the years ended December 31:



	2017		2016		2015
Beginning Balance	$	—	$	—	$	120
Total loss included in earnings		—		—		57
Exercises		—		—		(177)
Ending Balance	$	—	$	—	$	—

Acquisition-Related Contingent Consideration. Contingent consideration arrangements under the nContact merger agreement obligate the Company to pay former shareholders of nContact for the following milestones, if achieved:

Trial Enrollment Milestone – $7,500 upon completion of patient enrollment in the CONVERGE IDE clinical trial. Such payment is due within 30 days following enrollment of the final patient.

Regulatory Milestone – up to $42,500 upon the completion of the CONVERGE IDE clinical trial and receiving a PMA from FDA for the EPi-Sense AF Guided Coagulation System and/or any other nContact product with an indication for symptomatic persistent Afib or similar or related indication. The full contingent consideration amount of $42,500 is only earned if such regulatory approvals are received on or before January 1, 2020. The potential contingent consideration is reduced by 8.33% (or one-twelfth) each month following January 2020, and is reduced to zero if the regulatory milestone is achieved after December 31, 2020. Any payment of the regulatory milestone contingent consideration is due within 30 days following the receipt of the related PMA approval.

Commercial Milestone – for calendar years 2016 through 2019, nContact revenues in excess of specified target revenue amounts will result in contingent consideration equal to 1.5 times the revenues in excess of target. Payments of contingent consideration when the commercial milestone is achieved are due within 65 days of each calendar year end.

Subject to the terms and conditions of the merger agreement, all contingent consideration must be paid first in shares of AtriCure common stock. The merger agreement limits the total number of shares of AtriCure common stock issued in connection with the acquisition to 5,660, of which 3,757 shares were issued at closing of the nContact acquisition on October 13, 2015. Since the acquisition, no payments of contingent consideration have been required or made. As of December 31, 2017 and 2016, contingent consideration is recorded in other noncurrent liabilities in the Consolidated Balance Sheets.

The Company measures contingent consideration liabilities using unobservable inputs by applying an income approach, such as the discounted cash flow technique or the probability-weighted scenario method. Various key assumptions, such as the probability of achievement of the agreed milestones, projected revenues from acquisitions and the discount rate, are used in the determination of fair value of contingent consideration arrangements and are not observable in the market, thus representing a Level 3 measurement within the fair value hierarchy. Subsequent revisions to key assumptions, which impact the estimated fair value of contingent consideration liabilities, are reflected in the Consolidated Statements of Operations and Comprehensive Loss.

The fair value of the nContact contingent consideration was remeasured as of December 31, 2017, resulting in a decrease in fair value of $4,078. This decrease in fair value is due primarily to changes in estimates related to the timing of achievement of the regulatory milestone as a result of actual enrollment in the CONVERGE IDE clinical trial in 2017, offset partially by an increase in forecasted revenues for 2018 and 2019 under the commercial milestone payment. The fair value of contingent consideration increased $969 during the year ended December 31, 2016 due primarily to a reduction in the discount period. Adjustments to fair value are recorded in selling, general and administrative expenses in the accompanying Consolidated Statements of Operations and Comprehensive Loss.

The following table represents the company’s Level 3 fair value measurements using significant other unobservable inputs for acquisition-related contingent consideration for each of the years ended December 31:



	2017		2016		2015
Beginning Balance	$	41,176	$	40,207	$	—
Amounts acquired		—		—		40,207
Changes in fair value included in earnings		(4,078)		969		—
Ending Balance	$	37,098	$	41,176	$	40,207

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Investments

12 Months Ended

Dec. 31, 2017

Investments [Abstract]

Investments

4. INVESTMENTS

Investments as of December 31, 2017 consisted of the following:



			Unrealized
			Gains
	Cost Basis		(Losses)		Fair Value
Corporate bonds	$	2,925	$	(5)	$	2,920
U.S. government agencies and securities		3,000		(1)		2,999
Commercial paper		6,723		—		6,723
Total	$	12,648	$	(6)	$	12,642

Investments as of December 31, 2016 consisted of the following:



			Unrealized
			Gains
	Cost Basis		(Losses)		Fair Value
Corporate bonds	$	8,284	$	(8)	$	8,276
U.S. government agencies and securities		8,542		(13)		8,529
Commercial paper		5,996		—		5,996
Total	$	22,822	$	(21)	$	22,801

The Company has not experienced any significant realized gains or losses on its investments in the periods presented in the Consolidated Statements of Operations and Comprehensive Loss. Long term investments held by the Company at December 31, 2016 had maturities between one and two years.

Intangible Assets and Goodwill

12 Months Ended

Dec. 31, 2017

Intangible Assets and Goodwill [Abstract]

Intangible Assets and Goodwill

5. INTANGIBLE ASSETS AND GOODWILL

The following table provides a summary of the Company’s intangible assets at December 31:



		2017				2016
	Estimated			Accumulated				Accumulated
	Useful Life	Cost		Amortization		Cost		Amortization
Fusion technology	10 years	$	9,242	$	3,697	$	9,242	$	2,773
Clamp & probe technology	3 years		829		829		829		829
SUBTLE access technology	5 years		2,179		981		2,179		538
IPR&D			44,021		—		44,021		—
Total		$	56,271	$	5,507	$	56,271	$	4,140

Amortization expense related to intangible assets with definite lives, which excludes the IPR&D asset, was $1,367, $1,644 and $1,303 for the years ended December 31, 2017, 2016 and 2015.

Future amortization expense related to intangible assets with definite lives is projected as follows:



2018	$	1,367
2019		1,367
2020		1,235
2021		924
2022		925
2023 and thereafter		925
Total	$	6,743

The following table provides a summary of the Company’s goodwill, which is not amortized, but rather tested annually for impairment:



Net carrying amount as of December 31, 2015	$	105,257
Additions (Impairments)		—
Net carrying amount as of December 31, 2016		105,257
Additions (Impairments)		—
Net carrying amount as of December 31, 2017	$	105,257

Inventories

12 Months Ended

Dec. 31, 2017

Inventories [Abstract]

Inventories

6. INVENTORIES

Inventories consisted of the following at December 31:



	2017		2016
Raw materials	$	7,755	$	5,719
Work in process		1,299		1,221
Finished goods		13,397		10,720
Inventories	$	22,451	$	17,660

Property and Equipment

12 Months Ended

Dec. 31, 2017

Property and Equipment [Abstract]

Property and Equipment

7. PROPERTY AND EQUIPMENT

Property and equipment consisted of the following at December 31:



	Estimated Useful Life	2017		2016
Generators and other capital equipment	1 - 3 years	$	15,754	$	13,087
Building under capital lease	15 years		14,250		14,250
Computer and other office equipment	3 years		5,873		5,321
Machinery, equipment and vehicles	3 - 7 years		4,576		3,731
Furniture and fixtures	3 - 7 years		4,366		3,676
Leasehold improvements	5 - 15 years		3,636		3,319
Construction in progress	N/A		1,810		539
Equipment under capital leases	3 - 5 years		221		215
Total			50,486		44,138
Less accumulated depreciation			(21,737)		(14,143)
Property and equipment, net		$	28,749	$	29,995

Property and equipment depreciation expense was $7,761, $7,655 and $4,975 for the years ended December 31, 2017, 2016 and 2015. Depreciation related to generators and other capital equipment was $3,574, $3,591 and $2,944 in 2017, 2016 and 2015. As of December 31, 2017 and 2016, the net carrying value of generators and other capital equipment was $4,656 and $5,692.

Accrued Liabilities

12 Months Ended

Dec. 31, 2017

Accrued Liabilities [Abstract]

Accrued Liabilities

8. ACCRUED LIABILITIES

Accrued liabilities consisted of the following at December 31:



	2017		2016
Accrued commissions	$	6,964	$	5,737
Accrued bonus		4,726		2,871
Accrued payroll and employee-related expenses		4,097		4,326
Sales returns and allowances		1,169		834
Other accrued liabilities		695		929
Accrued taxes and value-added taxes payable		634		1,289
Accrued royalties		626		481
Total	$	18,911	$	16,467

Indebtedness

12 Months Ended

Dec. 31, 2017

Indebtedness [Abstract]

Indebtedness

9. INDEBTEDNESS

Credit Facility. The Company has a Loan and Security Agreement (Loan Agreement) with Silicon Valley Bank (SVB). The Loan Agreement, as amended, restated and modified, includes a $25,000 term loan and $15,000 revolving line of credit, both which mature in April 2021. Borrowing availability under the revolving credit facility is based on the lesser of $15,000 or a borrowing base calculation as defined by the Loan Agreement. As of December 31, 2017, the Company had no borrowings under the revolving credit facility and had borrowing availability of $15,000. The revolving line of credit is subject to an annual commitment fee of $50, and any borrowings thereunder bear interest at the Prime Rate. Financing costs related to the revolving line of credit are included in other assets in the Consolidated Balance Sheets and amortized ratably over the term of the Loan Agreement.

The term loan has a five-year term, with principal payments made ratably commencing eighteen months after the inception of the loan (November 2017) through the loan’s maturity date. The term loan accrues interest at the Prime Rate and is subject to an additional 4.0% fee on the original $25,000 principal amount at maturity or prepayment of the term loan. The Company is accruing the 4.0% fee over the term of the Loan Agreement. As of December 31, 2017, the Company has accrued $337 of this fee and included it in the outstanding loan balance in the Consolidated Balance Sheets. Other financing costs related to the term loan are net against the outstanding loan balance in the Consolidated Balance Sheets and amortized ratably over the term of the Loan Agreement.

The Loan Agreement also provides for certain prepayment and early termination fees, as well as establishes covenants related to liquidity, sales growth and a minimum cash balance, and includes other customary terms and conditions. Specified assets have been pledged as collateral.

Effective February 23, 2018, the Company and SVB entered into a Loan and Security Agreement which amends and restates the Company’s credit facility with SVB. The agreement provides for a $40,000 term loan, and $20,000 revolving line of credit with an option to increase the revolving line of credit by an additional $20,000. The Loan and Security Agreement credit facility has a five-year term, expiring February 2023. Principal payments of the term loan are to be made ratably commencing eighteen months after the inception of the loan through the loan’s maturity date. If the Company meets certain conditions, as specified by the agreement, the commencement of term loan principal payments may be deferred by an additional six months. The term loan accrues interest at the greater of the Prime Rate plus 3.75% or 8.25% and is subject to an additional 3.50% fee on the original $40,000 term loan principal amount at maturity. The revolving line of credit is subject to an annual facility fee of 0.33% of the revolving line of credit, and any borrowings bear interest at the greater of the Prime Rate and 4.50%. The Loan and Security Agreement also provides for certain prepayment and early termination fees, as well as establishes covenants related to sales growth, along with other customary terms and conditions similar to those in the Company’s current agreement with SVB. The proceeds from the agreement are expected to fund current and future operations of the Company. As a result of the refinancing, borrowings outstanding under the existing term loan agreement have been classified as long-term in the Consolidated Balance Sheet as of December 31, 2017.

Capital Lease Obligations. As of December 31, 2017, the Company had capital leases for its corporate headquarters building and computer equipment that expire at various terms through 2030. Capital lease assets are depreciated over their estimated useful lives. As of December 31, 2017, the cost of the leased assets, both building and computer equipment, was $14,471. Accumulated amortization on the capital lease assets was $2,249.

In connection with the terms of the Company’s corporate headquarters lease, a letter of credit in the amount of $1,250 was issued to the landlord of the building in October 2015. The letter of credit was renewed in June 2017 and remains outstanding as of December 31, 2017.

Future maturities on capital lease obligations and debt, after consideration of the refinancing transaction in February 2018, are projected as follows:



2018	$	1,468
2019		3,755
2020		8,305
2021		8,309
2022		8,335
2023 and thereafter		14,379
Total payments	$	44,551
Imputed interest on capital lease obligations		(7,129)
Net debt obligations, of which $561 is current and $36,861 is noncurrent	$	37,422

Commitments and Contingencies

12 Months Ended

Dec. 31, 2017

Commitments and Contingencies [Abstract]

Commitments and Contingencies

10. COMMITMENTS AND CONTINGENCIES

Lease Commitments. The Company leases certain office and warehouse facilities and a vehicle under noncancelable operating leases that expire at various terms through 2022. Future minimum lease payments under non-cancelable operating leases are projected as follows:



2018	$	965
2019		927
2020		737
2021		413
2022		306
2023 and thereafter		—
Total	$	3,348

Rent expense was approximately $850, $1,250 and $1,515 in 2017, 2016, and 2015.

Royalty Agreements. The Company has certain royalty agreements in place with terms that include payment of royalties based on product revenue from sales of specified current products. The current royalty agreements have effective dates as early as 2003 and terms ranging from eighteen years to at least twenty years. The royalties range from 3% to 5% of specified product sales. Parties to the royalty agreements have the right at any time to terminate the agreement immediately for cause. Royalty expense of $2,323, $1,895 and $1,799 was recorded as part of cost of revenue for the years ended December 31, 2017, 2016 and 2015.

Purchase Agreements. The Company enters into standard purchase agreements with certain vendors in the ordinary course of business. Outstanding commitments at December 31, 2017 were not significant.

Legal. The Company may, from time to time, become a party to legal proceedings. Such matters are subject to many uncertainties and to outcomes of which the financial impacts are not predictable with assurance and that may not be known for extended periods of time. When management has assessed that a loss is probable and an amount can be reasonably estimated, the Company records a liability in the Consolidated Financial Statements. Costs associated with legal proceedings could have a material adverse effect on the Company’s future consolidated results of operations, financial position, or cash flows.

On December 11, 2017, the Company received a Civil Investigative Demand (CID) from the U.S. Department of Justice stating that it is investigating the Company to determine whether the Company has violated the False Claims Act, relating to the promotion of certain medical devices related to the treatment of atrial fibrillation for off-label use and submitted or caused to be submitted false claims to certain federal and state health care programs for medically unnecessary healthcare services related to the treatment of atrial fibrillation. The CID covers the period from January 1, 2010 to the present and requires the production of documents and answers to written interrogatories. The Company had no knowledge of the investigation prior to receipt of the CID. The Company maintains rigorous policies and procedures to promote compliance with the False Claims Act and other applicable regulatory requirements, and is working with the U.S. Department of Justice to promptly respond to the CID. However, the Company cannot predict when the investigation will be resolved, the outcome of the investigation or its potential impact on the Company.

Income Taxes

12 Months Ended

Dec. 31, 2017

Income Taxes [Abstract]

Income Taxes

11. INCOME TAXES

The Company files federal, state, local and foreign income tax returns in jurisdictions with varying statutes of limitations. Income taxes are computed using the asset and liability method in accordance with FASB ASC 740, “Income Taxes”, under which deferred income taxes are provided for the temporary differences between the financial reporting basis and the tax basis of the Company’s assets and liabilities. Deferred taxes are measured using provisions of currently enacted tax laws. A valuation allowance against deferred tax assets is recorded when it is more likely than not that such assets will not be fully realized. The Company has recorded a full valuation allowance against substantially all net deferred tax assets as it is more likely than not that the benefit of the deferred tax assets will not be recognized in future periods. Tax credits are accounted for as a reduction of income taxes in the year in which the credit originates.

On December 22, 2017, H.R.1, “An Act to Provide for Reconciliation Pursuant to Titles II and V of the Concurrent Resolution on the Budget for Fiscal Year 2018” (the Tax Reform Act) was enacted, and amends the Internal Revenue Code to reduce tax rates and modify policies, credits, and deductions for individuals and businesses. For businesses, U.S. GAAP requires resulting tax effects of accounting for the Tax Reform Act to be recorded in the reporting period of enactment. Also on December 22, 2017, the SEC staff issued Staff Accounting Bulletin No. 118 (SAB 118) to address the application of U.S. GAAP in situations when a registrant does not have the necessary information available, prepared, or analyzed in reasonable detail to complete the accounting for certain income tax effects of the Tax Reform Act.

We have not completed our accounting for the tax effects of enactment of the Tax Reform Act. However, we have made a reasonable estimate of the effects on our existing deferred tax balances where possible, and accounted for material provisions of the Tax Reform Act as follows:

Reduction of US federal corporate tax rate: The Tax Reform Act reduces the corporate tax rate from 34 to 21 percent, effective January 1, 2018. Consequently, the Company has recorded a reduction to its federal deferred tax assets of $29,480 with an offsetting reduction in its valuation allowance at December 31, 2017. In addition, the Company’s state deferred tax assets and corresponding valuation allowance have been adjusted to account for the impact of the federal rate change on state deferred taxes.

Deemed Repatriation Transition Tax: The Tax Reform Act provides for a one-time "deemed repatriation" of accumulated foreign earnings for the year ended December 31, 2017. The Company does not anticipate a tax on the deemed repatriation as a result of its foreign deficits.

Compensation and Shared-Based Payment Awards: The Tax Reform Act modifies the deductibility of covered employees’ compensation and eliminates the exclusion of performance-based compensation under IRC § 162(m), prospectively. The Tax Reform Act includes a transition rule that permits the continued exclusion of performance-based compensation paid pursuant to a written, binding contract which was in effect on November 2, 2017, and which was not modified in any material respect on or after such date. The Company has not completed its analysis of all of its relevant equity compensation agreements to determine if the transition rule will apply and the deferred tax implications of this provision.

Corporate Alternative Minimum Tax (AMT): The repeal of AMT provides companies with the ability to obtain refunds of historic AMT credits. The Company has recorded a deferred tax benefit of $102 associated with release of its valuation allowance on its AMT credits.

Bonus Depreciation: The Tax Reform Act provides for 100 percent bonus depreciation on personal tangible property expenditures beginning September 27, 2017 through 2022. The bonus depreciation percentage is phased down from 100 percent beginning in 2023 through 2026. The Company is continuing to evaluate its bonus depreciation election based on an analysis of property eligible for 100 percent bonus depreciation and its net operating loss carryforwards.

The Company expects to complete the accounting for the Tax Reform Act when the 2017 U.S. corporate income tax return is filed in 2018. The ultimate impact may differ materially from these provisional amounts due to additional analysis, changes in interpretations and assumptions the Company has made, additional regulatory guidance that may be issued, and actions the Company may take as a result of the Tax Reform Act.

The detail of deferred tax assets and liabilities at December 31 is as follows:



	2017		2016
Deferred tax assets (liabilities):
Net operating loss carryforward	$	64,776	$	84,056
Research and development and AMT credit carryforwards, net		5,339		5,446
Equity compensation		6,955		8,406
Accruals and reserves		874		914
Inventories		588		1,503
Intangible assets		(11,297)		(16,922)
Property and equipment, net		(339)		(1,487)
Other, net		179		66
Subtotal		67,075		81,982
Less valuation allowance		(66,973)		(81,982)
Total	$	102	$	—

The Company’s provision for income taxes for each of the years ended December 31 is as follows:



	2017		2016		2015
Current Tax Expense
Federal	$	—	$	—	$	2
State		44		32		34
Foreign		72		8		—
Total current tax expense		116		40		36
Deferred Tax Expense
Federal	$	18,485	$	(7,333)	$	(7,154)
State		(1,337)		210		(398)
Foreign		(2,241)		(1,177)		(955)
Change in valuation allowance		(15,009)		8,300		8,507
Total deferred tax expense		(102)		—		—
Total tax expense	$	14	$	40	$	36

The Company has federal net operating loss carryforwards of $240,286 which have expirations between 2021 and 2038 and state net operating loss carryforwards of $147,841 with varying expirations from 2018 to 2038. At December 31, 2016, there were $2,816 of unrecognized deferred tax assets that arose from tax deductions for equity compensation in excess of compensation recognized for financial reporting during years when net operating losses were created. On January 1, 2017, the Company adopted ASU 2016-09, “Improvements to Employee Share-Based Payment Accounting” and recognized $2,816 of previously unrecognized deferred tax assets with a corresponding increase in its valuation allowance. A portion of the Company’s federal and state net operating loss carryforwards are subject to certain limitations under Internal Revenue Code Sections 382 and 383. The Company has federal research and development credit carryforwards of $6,392 which have expirations between 2022 and 2038. Additionally, the Company has foreign net operating loss carryforwards of approximately $30,501 which have expirations between 2018 and 2027.

The Company’s 2017, 2016 and 2015 effective income tax rates differ from the federal statutory rate as follows:



	2017				2016				2015
Federal tax at statutory rate	34.00	%	$	(9,139)	34.00	%	$	(11,322)	34.00	%	$	(9,240)
Federal tax rate change	(109.68)			29,480
Federal R&D credit	(0.40)			107	2.89			(962)	3.23			(878)
Federal NOL adjustment for ASU	10.48			(2,816)
Valuation allowance	55.84			(15,009)	(24.93)			8,300	(31.30)			8,507
State income taxes	4.81			(1,292)	(0.69)			231	1.38			(375)
Foreign NOL rate change	1.30			(348)	(1.36)			452	(2.02)			549
Foreign tax rate differential	(2.45)			658	(1.62)			539	(1.99)			542
Permanent differences and other	6.05			(1,627)	(8.41)			2,802	(3.43)			931
Effective tax rate	(0.05)	%	$	14	(0.12)	%	$	40	(0.13)	%	$	36

The Company’s pre-tax book loss for domestic and international operations, respectively, was $(19,409) and $(7,469) for 2017, ($27,271) and ($6,027) for 2016 and ($21,157) and ($6,019) for 2015. The Company had undistributed earnings of foreign subsidiaries of approximately $107 at December 31, 2017. The Company does not consider these earnings as permanently reinvested and thus has recognized appropriate U.S. current and deferred taxes on such amounts.

Federal, state, and local tax returns of the Company are routinely subject to examination by various taxing authorities. Federal income tax returns for periods beginning in 2015 are open for examination. Generally, state and foreign income tax returns for periods beginning in 2014 are open for examination. However, taxing authorities have the ability to adjust net operating loss and tax credit carryforwards from years prior to these periods. The Company has not recognized certain tax benefits because of the uncertainty of realizing the entire value of the tax position taken on income tax returns upon review by the taxing authorities.

A reconciliation of the change in federal and state unrecognized tax benefits for 2017, 2016 and 2015 is presented below:



	2017		2016		2015
Balance at the beginning of the year	$	3,175	$	1,982	$	1,982
Increases (decreases) for prior year tax positions		(2,018)		1,193		—
Increases (decreases) for current year tax positions		—		—		—
Increases (decreases) related to settlements		—		—		—
Decreases related to statute lapse		—		—		—
Balance at the end of the year	$	1,157	$	3,175	$	1,982

The Internal Revenue Service completed its review of the Company’s 2014 federal income tax return in February 2017. In 2017, the Company also completed a detailed analysis of R&D credit carryforwards for the tax years 2008 through 2016. As a result of this analysis, as well as completion of the IRS audit of the 2014 credit, the Company has reduced both the R&D credit carryforward and related unrecognized tax benefits by $2,018. The Company has not had to accrue any interest and penalties related to unrecognized income tax benefits as a result of offsetting of net operating losses. However, if the situation occurs, the Company will recognize interest and penalties within the income tax expense line in the Consolidated Statements of Operations and Comprehensive Loss and within the related tax liability line in the Consolidated Balance Sheets.

There are no amounts included in the balance of unrecognized tax benefits at December 31, 2017, 2016 and 2015 that, if recognized, would affect the effective tax rate. Included in the balance of unrecognized tax benefits at December 31, 2017 are $1,157 of tax benefits that, if recognized, would result in adjustments to other tax accounts, primarily deferred taxes and valuation allowance. The Company does not expect that its unrecognized tax benefits for research credits will significantly change within twelve months of December 31, 2017.

Concentrations	12 Months Ended
Concentrations	Dec. 31, 2017
Concentrations [Abstract]
Concentrations	12. CONCENTRATIONS During 2017, 2016 and 2015, approximately 13.2%, 14.4% and 12.9%, of the Company’s total net revenue was derived from its top ten customers. During 2017, 2016 and 2015 no individual customer accounted for more than 10% of the Company’s revenue. As of December 31, 2017 and 2016, 19.7% and 19.9% of the Company’s total accounts receivable balance was derived from its top ten customers. No individual customer accounted for more than 10% of the Company’s accounts receivable as of December 31, 2017 and 2016. The Company maintains cash and cash equivalents balances at financial institutions which at times exceed FDIC limits. As of December 31, 2017, $21,360 of the cash and cash equivalents balance was in excess of the FDIC limits.

Employee Benefit Plans	12 Months Ended
Employee Benefit Plans	Dec. 31, 2017
Employee Benefit Plans [Abstract]
Employee Benefit Plans	13. EMPLOYEE BENEFIT PLANS The Company sponsors the AtriCure, Inc. 401(k) Plan (401(k) Plan), a defined contribution plan covering substantially all U.S. employees of the Company. Eligible employees may contribute pre-tax annual compensation up to specified maximums under the Internal Revenue Code. During 2017, 2016 and 2015 the Company made matching contributions of 50% of the first 6% of employee contributions to the 401(k) Plan. The Company’s matching contributions expensed during 2017, 2016 and 2015 were $1,367, $1,222 and $1,007. Additional amounts may be contributed to the 401(k) Plan at the discretion of the Company’s Board of Directors, however, no such discretionary contributions were made during 2017, 2016 or 2015. The Company also provides retirement benefits for employees of AtriCure Europe and other foreign subsidiaries. Total contributions to retirement plans for these employees were $205, $101 and $133 in 2017, 2016 and 2015.

Equity Compensation Plans

12 Months Ended

Dec. 31, 2017

Equity Compensation Plans [Abstract]

Equity Compensation Plans

14. EQUITY COMPENSATION PLANS

The Company has two share-based incentive plans: the 2014 Stock Incentive Plan (2014 Plan) and the 2008 Employee Stock Purchase Plan (ESPP).

Stock Incentive Plan

Under the 2014 Plan, the Board of Directors may grant incentive stock options to Company employees and may grant nonstatutory stock options, restricted stock or stock appreciation rights to Company employees, directors and consultants. The administrator (currently the Compensation Committee of the Board of Directors) has the authority to determine the terms of any awards, including the number of shares subject to each award, the exercisability of the awards and the form of consideration. As of December 31, 2017, 10,249 shares of common stock had been reserved for issuance under the 2014 Plan and 1,128 shares were available for future grants.

Options granted under the 2014 Plan generally expire ten years from the date of grant and generally vest at a rate of 25% on the first anniversary date of the grant and ratably each month thereafter over the following three years. Restricted stock awards granted under the 2014 Plan vest between one and four years from the date of grant.

Activity under the plans during 2017 was as follows:


				Weighted
			Weighted	Average
	Number of		Average	Remaining		Aggregate
	Shares		Exercise	Contractual		Intrinsic
Time-Based Stock Options	Outstanding		Price	Term		Value
Outstanding at January 1, 2017	2,454	$	12.51
Granted	65		20.22
Exercised	(458)		9.61
Cancelled	(35)		19.08
Outstanding at December 31, 2017	2,026	$	13.30	5.62	$	11,730
Vested and expected to vest	2,004	$	13.23	5.58	$	11,717
Exercisable at December 31, 2017	1,766	$	12.48	5.20	$	11,471


			Weighted
	Number of		Average
	Shares		Grant Date
Restricted Stock	Outstanding		Fair Value
Outstanding at January 1, 2017	1,416	$	17.40
Awarded	771		19.38
Released	(331)		17.43
Forfeited	(11)		18.52
Outstanding at December 31, 2017	1,845	$	18.22


				Weighted
			Weighted	Average
	Number of		Average	Remaining		Aggregate
	Shares		Exercise	Contractual		Intrinsic
Performance Stock Options	Outstanding		Price	Term		Value
Outstanding at January 1, 2017	450	$	13.48
Granted	—		—
Exercised	—		—
Cancelled	—		—
Outstanding at December 31, 2017	450	$	13.48	5.45	$	2,774
Exercisable at December 31, 2017	250	$	13.48	5.45	$	1,541

Activity under the plans during 2016 was as follows:



				Weighted
			Weighted	Average
	Number of		Average	Remaining		Aggregate
	Shares		Exercise	Contractual		Intrinsic
Time-Based Stock Options	Outstanding		Price	Term		Value
Outstanding at January 1, 2016	2,734	$	11.75
Granted	215		16.74
Exercised	(394)		8.47
Cancelled	(101)		16.66
Outstanding at December 31, 2016	2,454	$	12.51	6.02	$	18,295
Vested and expected to vest	2,420	$	12.42	5.99	$	18,228
Exercisable at December 31, 2016	1,914	$	11.01	5.40	$	16,897


			Weighted
	Number of		Average
	Shares		Grant Date
Restricted Stock	Outstanding		Fair Value
Outstanding at January 1, 2016	1,071	$	17.30
Awarded	710		16.35
Forfeited	(70)		17.31
Released	(295)		14.49
Outstanding at December 31, 2016	1,416	$	17.40


				Weighted
			Weighted	Average
	Number of		Average	Remaining		Aggregate
	Shares		Exercise	Contractual		Intrinsic
Performance Stock Options	Outstanding		Price	Term		Value
Outstanding at January 1, 2016	450	$	13.48
Granted	—		—
Exercised	—		—
Cancelled	—		—
Outstanding at December 31, 2016	450	$	13.48	6.45	$	3,074
Exercisable at December 31, 2016	250	$	13.48	6.45	$	1,708

The total intrinsic value of options exercised during the years ended December 31, 2017, 2016 and 2015 was $5,121, $3,550 and $2,740. As a result of the Company’s full valuation allowance on its net deferred tax assets, no tax benefit was recognized related to the stock option exercises. The exercise price per share of each option is equal to the fair market value of the underlying share on the date of grant. For 2017, 2016 and 2015, $4,402, $3,337 and $2,703 in cash proceeds were included in the Company’s Consolidated Statements of Cash Flows as a result of the exercise of stock options. The total fair value of restricted stock vested during 2017, 2016 and 2015 was $6,235, $5,102 and $2,767. The Company issues registered shares of common stock to satisfy stock option exercises and restricted stock grants.

The Company recognized expense related to time-based stock options and restricted stock for 2017, 2016, and 2015 of $13,908, $10,872 and $8,072. As of December 31, 2017 there was $23,331 of unrecognized compensation costs related to non-vested stock option and restricted stock arrangements ($2,197 relating to stock options and $21,134 relating to restricted stock). This cost is expected to be recognized over a weighted-average period of 2.2 years for stock options and 2.2 years for restricted stock.

The Company has awarded 450 performance options to its President and Chief Executive Officer. The options expire ten years from the date of grant and vest in increments of 25 shares when the volume adjusted weighted average closing price of the common stock of the Company as reported by NASDAQ (or any other exchange on which the common stock of the Company is listed) for 30 consecutive days equals or exceeds each of $10.00 per share, $12.50 per share, $15.00 per share, $17.50 per share, $20.00 per share, $25.00 per share, $30.00 per share, $35.00 per share and $40.00 per share. In accordance with FASB ASC 718, a Monte Carlo simulation was performed to estimate the fair values, vesting terms and vesting probabilities for each tranche of options. Expense calculated using these estimates is being recorded over the estimated vesting terms. The Company recognized expense related to the performance options during 2017, 2016 and 2015 of $43, $269 and $546. As of December 31, 2017, compensation costs related to non-vested performance options were fully recognized.

Employee Stock Purchase Plan

The ESPP is available to eligible employees as defined in the plan document. Under the ESPP, shares of the Company’s common stock may be purchased at a discount (currently 15%) of the lesser of the closing price of the Company’s common stock on the first trading day or the last trading day of the offering period. The offering period (currently six months) and the offering price are subject to change. Participants may not purchase more than $25 of the Company’s common stock in a calendar year and may not purchase a value of more than 3 shares during an offering period. On the first day of each fiscal year during the term of the ESPP, the number of shares available for sale under the ESPP may be increased by the lesser of (i) two percent (2%) of the Company’s outstanding shares of common stock as of the close of business on the last business day of the prior calendar year, not to exceed 600 shares, or (ii) a lesser amount determined by the Board of Directors. Shares have not been added to the ESPP since 2011. As of December 31, 2017, there were 225 shares available for future issuance under the ESPP. Share-based compensation expense with respect to the ESPP was $664, $556 and $379 for 2017, 2016 and 2015.

Valuation and Expense Information Under FASB ASC 718

The following table summarizes share-based compensation expense related to employees, directors and consultants under FASB ASC 718 for 2017, 2016 and 2015. The expense was allocated as follows:



	2017		2016		2015
Cost of revenue	$	610	$	420	$	416
Research and development expenses		2,052		1,825		1,373
Selling, general and administrative expenses		11,953		9,452		7,208
Total	$	14,615	$	11,697	$	8,997

In calculating compensation expense, the fair value of the options is estimated on the grant date using the Black-Scholes model including the following assumptions:



	2017		2016		2015
Risk-free interest rate	1.75 - 2.12	%	1.06 - 2.02	%	1.30 - 1.96	%
Expected life of option (years)	5.21 to 5.76		5.27 to 7.10		5.20 to 6.89
Expected volatility of stock	43.00 - 48.00	%	46.00 - 51.00	%	46.00 - 67.00	%
Weighted-average volatility	44.50	%	48.87	%	54.75	%
Dividend yield	0.00	%	0.00	%	0.00	%

The Company’s estimate of volatility is based solely on the Company’s trading history over the expected option life. The risk-free interest rate assumption is based upon the U.S. treasury yield curve at the time of grant for the expected option life. The Company estimates the expected terms of options using historical employee exercise behavior.

The fair value of restricted stock awards is based on the market value of the Company’s stock on the date of the awards.

Based on the assumptions noted above, the weighted average estimated grant date fair value per share of the stock options and restricted stock granted for 2017, 2016 and 2015 was as follows:



	2017		2016		2015
Stock options	$	8.60	$	8.25	$	11.12
Restricted stock		19.38		16.35		17.82

In calculating compensation expense for performance options, the fair value of the options was estimated on the grant dates using a Monte Carlo simulation including strike prices of $5.91 and $21.04, contractual terms of 10 years, expected volatility of 69.60% and 60.50% and interest rates of 1.75% and 2.73%. The contractual term assumes that the performance options issued to the CEO of the Company will be held until expiration. Expected volatility was estimated based on the Company’s trading history over the expected option life. The expected rate of return assumption was based upon the U.S. treasury yield curve at the time of grant for the expected option life.

Based on the assumptions noted above, the estimated grant date fair value per share of the performance options granted were as follows:



	Price		Fair Value of		Fair Value of
	Target		2012 Grant		2014 Grant
Tranche 1	$	10.00	$	4.32	$	14.74
Tranche 2		12.50		4.30		14.74
Tranche 3		15.00		4.27		14.74
Tranche 4		17.50		4.23		14.74
Tranche 5		20.00		4.19		14.73
Tranche 6		25.00		4.10		14.73
Tranche 7		30.00		4.01		14.71
Tranche 8		35.00		3.92		14.67
Tranche 9		40.00		3.83		14.61

Segment and Geographic Information

12 Months Ended

Dec. 31, 2017

Segment and Geographic Information [Abstract]

Segment and Geographic Information

15. SEGMENT AND GEOGRAPHIC INFORMATION

The Company evaluates reporting segments in accordance with FASB ASC 280, “Segment Reporting”. The Company develops, manufactures, and sells devices designed primarily for the surgical ablation of cardiac tissue and systems designed for the exclusion of the left atrial appendage. These devices are developed and marketed to a broad base of medical centers globally. Management considers all such sales to be part of a single operating segment. Revenue attributed to geographic areas is based on the location of the customers to whom products are sold.

Revenue by geographic area was as follows:



	2017		2016		2015
United States	$	138,387	$	122,385	$	102,212
Europe		21,901		19,772		17,180
Asia		13,616		12,223		9,510
Other international		812		729		853
Total international		36,329		32,724		27,543
Total revenue	$	174,716	$	155,109	$	129,755

United States revenue by product type was as follows:



	2017		2016		2015
Open-heart ablation	$	64,517	$	58,050	$	53,541
Minimally invasive ablation		34,421		31,169		21,564
AtriClip devices		37,281		30,321		24,377
Total ablation and AtriClip devices		136,219		119,540		99,482
Valve tools		2,168		2,845		2,730
Total United States	$	138,387	$	122,385	$	102,212

International revenue by product type was as follows:



	2017		2016		2015
Open-heart ablation	$	20,718	$	20,189	$	16,287
Minimally invasive ablation		8,007		8,065		7,964
AtriClip devices		7,251		3,986		2,868
Total ablation and AtriClip devices		35,976		32,240		27,119
Valve tools		353		484		424
Total international	$	36,329	$	32,724	$	27,543

The Company’s long-lived assets are located primarily in the United States, except for $957 as of December 31, 2017 and $931 as of December 31, 2016, which are located primarily in Europe.

Selected Quarterly Financial Data (Unaudited)

12 Months Ended

Dec. 31, 2017

Selected Quarterly Financial Data [Abstract]

Selected Quarterly Financial Data (Unaudited)

16. SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED)



	For the Three Months Ended
	March 31,				June 30,				September 30,				December 31,
	2017		2016		2017		2016		2017		2016		2017		2016
Operating Results:
Revenue	$	41,273	$	35,940	$	45,231	$	39,672	$	42,150	$	38,340	$	46,062	$	41,157
Gross profit		30,008		25,914		32,554		28,818		30,918		27,472		32,683		28,897
Loss from operations		(9,642)		(9,419)		(6,355)		(7,738)		(6,847)		(6,286)		(2,135)		(7,695)
Net loss		(10,183)		(9,724)		(6,883)		(8,206)		(7,246)		(6,783)		(2,580)		(8,625)
Net loss per share (basic and diluted)	$	(0.32)	$	(0.31)	$	(0.21)	$	(0.26)	$	(0.22)	$	(0.21)	$	(0.08)	$	(0.27)

Amounts may not sum to consolidated totals for the full year due to rounding. Basic and diluted net loss per share is computed independently for each of the quarters presented. Therefore, the sum of the quarterly per share amounts will not necessarily equal the total for the year.

Schedule II - Valuation And Qualifying Accounts

12 Months Ended

Dec. 31, 2017

Valuation and Qualifying Accounts [Abstract]

Schedule of Valuation and Qualifying Accounts Disclosure

SCHEDULE II

VALUATION AND QUALIFYING ACCOUNTS



	Beginning						Ending
	Balance		Additions		Deductions		Balance
Reserve for sales returns and allowances
Year ended December 31, 2017	$	834	$	441	$	106	$	1,169
Year ended December 31, 2016		207		634		7		834
Year ended December 31, 2015		135		78		6		207
Allowance for inventory valuation
Year ended December 31, 2017	$	1,080	$	1,004	$	1,195	$	889
Year ended December 31, 2016		843		1,692		1,455		1,080
Year ended December 31, 2015		522		720		399		843
Valuation allowance for deferred tax assets
Year ended December 31, 2017	$	81,982	$	—	$	15,009	$	66,973
Year ended December 31, 2016		73,682		8,300		—		81,982
Year ended December 31, 2015		59,554		14,128		—		73,682

Description of Business and Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2017

Description of Business and Summary of Significant Accounting Policies [Abstract]

Nature of the Business

Principles of Consolidation

Cash and Cash Equivalents

Investments

Revenue Recognition

Sales Returns and Allowances

Allowance for Doubtful Accounts Receivable

Inventories

Property and Equipment

Intangible Assets

Intangible Assets—Intangible assets with determinable useful lives are amortized on a straight-line basis over the estimated periods benefited (see Note 5).

The Company reviews intangible assets for impairment using its best estimates based on reasonable and supportable assumptions and projections.

Goodwill

Other Noncurrent Liabilities

Other Income (Expense)

Taxes

Net Loss Per Share

Comprehensive Income (Loss) and Accumulated Other Comprehensive Income (Loss)

Accumulated other comprehensive income (loss) consisted of the following (net of tax):



	2017		2016		2015
Total accumulated other comprehensive loss at beginning of period	$	(468)	$	(611)	$	(348)
Unrealized losses on investments
Balance at beginning of period	$	(21)	$	(39)	$	(54)
Other comprehensive income before reclassifications		15		18		15
Amounts reclassified from accumulated other comprehensive income (loss) to other income (loss)		—		—		—
Balance at end of period	$	(6)	$	(21)	$	(39)
Foreign currency translation adjustment
Balance at beginning of period	$	(447)	$	(572)	$	(294)
Other comprehensive income before reclassifications		660		532		156
Amounts reclassified from accumulated other comprehensive income (loss) to other income (loss)		(173)		(407)		(434)
Balance at end of period	$	40	$	(447)	$	(572)
Total accumulated other comprehensive income (loss) at end of period	$	34	$	(468)	$	(611)

Research and Development Costs

Advertising Costs

Advertising Costs— The Company expenses advertising costs as incurred. Advertising expense was $900, $625 and $476 during the years ended December 31, 2017, 2016 and 2015.

Share-Based Compensation

The Company estimates the fair value of restricted stock based upon the grant date closing market price of the Company’s common stock.

Use of Estimates

Fair Value Disclosures

Description of Business and Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2017

Description of Business and Summary of Significant Accounting Policies [Abstract]

Accumulated Other Comprehensive Income (Loss)



	2017		2016		2015
Total accumulated other comprehensive loss at beginning of period	$	(468)	$	(611)	$	(348)
Unrealized losses on investments
Balance at beginning of period	$	(21)	$	(39)	$	(54)
Other comprehensive income before reclassifications		15		18		15
Amounts reclassified from accumulated other comprehensive income (loss) to other income (loss)		—		—		—
Balance at end of period	$	(6)	$	(21)	$	(39)
Foreign currency translation adjustment
Balance at beginning of period	$	(447)	$	(572)	$	(294)
Other comprehensive income before reclassifications		660		532		156
Amounts reclassified from accumulated other comprehensive income (loss) to other income (loss)		(173)		(407)		(434)
Balance at end of period	$	40	$	(447)	$	(572)
Total accumulated other comprehensive income (loss) at end of period	$	34	$	(468)	$	(611)

Fair Value (Tables)

12 Months Ended

Dec. 31, 2017

Fair Value [Abstract]

Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis

The following table represents the Company’s fair value hierarchy for its financial assets and liabilities measured at fair value on a recurring basis as of December 31, 2017:



	Quoted Prices
	in Active		Significant		Significant
	Markets for		Other		Other
	Identical		Observable		Unobservable
	Assets		Inputs		Inputs
	(Level 1)		(Level 2)		(Level 3)		Total
Assets:
Money market funds	$	—	$	12,774	$	—	$	12,774
Commercial paper		—		7,472		—		7,472
U.S. government agencies and securities		2,999		—		—		2,999
Corporate bonds		—		2,920		—		2,920
Total assets	$	2,999	$	23,166	$	—	$	26,165
Liabilities:
Acquisition-related contingent consideration	$	—	$	—	$	37,098	$	37,098
Total liabilities	$	—	$	—	$	37,098	$	37,098

The following table represents the Company’s fair value hierarchy for its financial assets and liabilities measured at fair value on a recurring basis as of December 31, 2016:



	Quoted Prices
	in Active		Significant		Significant
	Markets for		Other		Other
	Identical		Observable		Unobservable
	Assets		Inputs		Inputs
	(Level 1)		(Level 2)		(Level 3)		Total
Assets:
Money market funds	$	—	$	17,085	$	—	$	17,085
Commercial paper		—		5,996		—		5,996
U.S. government agencies and securities		7,000		1,529		—		8,529
Corporate bonds		—		8,276		—		8,276
Total assets	$	7,000	$	32,886	$	—	$	39,886
Liabilities:
Acquisition-related contingent consideration	$	—	$	—	$	41,176	$	41,176
Total liabilities	$	—	$	—	$	41,176	$	41,176

Level 3 Fair Value Measurements Using Significant Other Unobservable Inputs for Derivative Instruments



	2017		2016		2015
Beginning Balance	$	—	$	—	$	120
Total loss included in earnings		—		—		57
Exercises		—		—		(177)
Ending Balance	$	—	$	—	$	—

Level 3 Fair Value Measurements Using Significant Other Unobservable Inputs for Acquisition-Related Contingent Consideration



	2017		2016		2015
Beginning Balance	$	41,176	$	40,207	$	—
Amounts acquired		—		—		40,207
Changes in fair value included in earnings		(4,078)		969		—
Ending Balance	$	37,098	$	41,176	$	40,207

Investments (Tables)

12 Months Ended

Dec. 31, 2017

Investments [Abstract]

Summary of Short-term Investments

Investments as of December 31, 2017 consisted of the following:



			Unrealized
			Gains
	Cost Basis		(Losses)		Fair Value
Corporate bonds	$	2,925	$	(5)	$	2,920
U.S. government agencies and securities		3,000		(1)		2,999
Commercial paper		6,723		—		6,723
Total	$	12,648	$	(6)	$	12,642

Investments as of December 31, 2016 consisted of the following:



			Unrealized
			Gains
	Cost Basis		(Losses)		Fair Value
Corporate bonds	$	8,284	$	(8)	$	8,276
U.S. government agencies and securities		8,542		(13)		8,529
Commercial paper		5,996		—		5,996
Total	$	22,822	$	(21)	$	22,801

Intangible Assets and Goodwill (Tables)

12 Months Ended

Dec. 31, 2017

Intangible Assets and Goodwill [Abstract]

Company's Intangible Assets



		2017				2016
	Estimated			Accumulated				Accumulated
	Useful Life	Cost		Amortization		Cost		Amortization
Fusion technology	10 years	$	9,242	$	3,697	$	9,242	$	2,773
Clamp & probe technology	3 years		829		829		829		829
SUBTLE access technology	5 years		2,179		981		2,179		538
IPR&D			44,021		—		44,021		—
Total		$	56,271	$	5,507	$	56,271	$	4,140

Future Amortization Expense Related to Intangible Assets with Definite Lives



2018	$	1,367
2019		1,367
2020		1,235
2021		924
2022		925
2023 and thereafter		925
Total	$	6,743

Summary of Company's Goodwill



Net carrying amount as of December 31, 2015	$	105,257
Additions (Impairments)		—
Net carrying amount as of December 31, 2016		105,257
Additions (Impairments)		—
Net carrying amount as of December 31, 2017	$	105,257

Inventories (Tables)

12 Months Ended

Dec. 31, 2017

Inventories [Abstract]

Summary Of Inventories



	2017		2016
Raw materials	$	7,755	$	5,719
Work in process		1,299		1,221
Finished goods		13,397		10,720
Inventories	$	22,451	$	17,660

Property and Equipment (Tables)

12 Months Ended

Dec. 31, 2017

Property and Equipment [Abstract]

Summary of Property and Equipment



	Estimated Useful Life	2017		2016
Generators and other capital equipment	1 - 3 years	$	15,754	$	13,087
Building under capital lease	15 years		14,250		14,250
Computer and other office equipment	3 years		5,873		5,321
Machinery, equipment and vehicles	3 - 7 years		4,576		3,731
Furniture and fixtures	3 - 7 years		4,366		3,676
Leasehold improvements	5 - 15 years		3,636		3,319
Construction in progress	N/A		1,810		539
Equipment under capital leases	3 - 5 years		221		215
Total			50,486		44,138
Less accumulated depreciation			(21,737)		(14,143)
Property and equipment, net		$	28,749	$	29,995

Accrued Liabilities (Tables)

12 Months Ended

Dec. 31, 2017

Accrued Liabilities [Abstract]

Accrued Liabilities



	2017		2016
Accrued commissions	$	6,964	$	5,737
Accrued bonus		4,726		2,871
Accrued payroll and employee-related expenses		4,097		4,326
Sales returns and allowances		1,169		834
Other accrued liabilities		695		929
Accrued taxes and value-added taxes payable		634		1,289
Accrued royalties		626		481
Total	$	18,911	$	16,467

Indebtedness (Tables)

12 Months Ended

Dec. 31, 2017

Indebtedness [Abstract]

Future Maturities On Debt And Capital Lease Obligations



2018	$	1,468
2019		3,755
2020		8,305
2021		8,309
2022		8,335
2023 and thereafter		14,379
Total payments	$	44,551
Imputed interest on capital lease obligations		(7,129)
Net debt obligations, of which $561 is current and $36,861 is noncurrent	$	37,422

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2017

Commitments and Contingencies [Abstract]

Future Minimum Lease Payments Under Non-cancelable Operating Leases



2018	$	965
2019		927
2020		737
2021		413
2022		306
2023 and thereafter		—
Total	$	3,348

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

Income Taxes [Abstract]

Summary of Detail of Deferred Tax Assets and Liabilities



	2017		2016
Deferred tax assets (liabilities):
Net operating loss carryforward	$	64,776	$	84,056
Research and development and AMT credit carryforwards, net		5,339		5,446
Equity compensation		6,955		8,406
Accruals and reserves		874		914
Inventories		588		1,503
Intangible assets		(11,297)		(16,922)
Property and equipment, net		(339)		(1,487)
Other, net		179		66
Subtotal		67,075		81,982
Less valuation allowance		(66,973)		(81,982)
Total	$	102	$	—

Summary Of Company's Provision for Income Taxes



	2017		2016		2015
Current Tax Expense
Federal	$	—	$	—	$	2
State		44		32		34
Foreign		72		8		—
Total current tax expense		116		40		36
Deferred Tax Expense
Federal	$	18,485	$	(7,333)	$	(7,154)
State		(1,337)		210		(398)
Foreign		(2,241)		(1,177)		(955)
Change in valuation allowance		(15,009)		8,300		8,507
Total deferred tax expense		(102)		—		—
Total tax expense	$	14	$	40	$	36

Summary Of Difference Between Effective Income Tax Rates and Federal Statutory Rate



	2017				2016				2015
Federal tax at statutory rate	34.00	%	$	(9,139)	34.00	%	$	(11,322)	34.00	%	$	(9,240)
Federal tax rate change	(109.68)			29,480
Federal R&D credit	(0.40)			107	2.89			(962)	3.23			(878)
Federal NOL adjustment for ASU	10.48			(2,816)
Valuation allowance	55.84			(15,009)	(24.93)			8,300	(31.30)			8,507
State income taxes	4.81			(1,292)	(0.69)			231	1.38			(375)
Foreign NOL rate change	1.30			(348)	(1.36)			452	(2.02)			549
Foreign tax rate differential	(2.45)			658	(1.62)			539	(1.99)			542
Permanent differences and other	6.05			(1,627)	(8.41)			2,802	(3.43)			931
Effective tax rate	(0.05)	%	$	14	(0.12)	%	$	40	(0.13)	%	$	36

Summary Of Reconciliation of Change in Federal and State Unrecognized Tax Benefits



	2017		2016		2015
Balance at the beginning of the year	$	3,175	$	1,982	$	1,982
Increases (decreases) for prior year tax positions		(2,018)		1,193		—
Increases (decreases) for current year tax positions		—		—		—
Increases (decreases) related to settlements		—		—		—
Decreases related to statute lapse		—		—		—
Balance at the end of the year	$	1,157	$	3,175	$	1,982

Equity Compensation Plans (Tables)

12 Months Ended

Dec. 31, 2017

Equity Compensation Plans [Abstract]

Activity Under Stock Based Compensation Plans

Activity under the plans during 2017 was as follows:


				Weighted
			Weighted	Average
	Number of		Average	Remaining		Aggregate
	Shares		Exercise	Contractual		Intrinsic
Time-Based Stock Options	Outstanding		Price	Term		Value
Outstanding at January 1, 2017	2,454	$	12.51
Granted	65		20.22
Exercised	(458)		9.61
Cancelled	(35)		19.08
Outstanding at December 31, 2017	2,026	$	13.30	5.62	$	11,730
Vested and expected to vest	2,004	$	13.23	5.58	$	11,717
Exercisable at December 31, 2017	1,766	$	12.48	5.20	$	11,471


			Weighted
	Number of		Average
	Shares		Grant Date
Restricted Stock	Outstanding		Fair Value
Outstanding at January 1, 2017	1,416	$	17.40
Awarded	771		19.38
Released	(331)		17.43
Forfeited	(11)		18.52
Outstanding at December 31, 2017	1,845	$	18.22


				Weighted
			Weighted	Average
	Number of		Average	Remaining		Aggregate
	Shares		Exercise	Contractual		Intrinsic
Performance Stock Options	Outstanding		Price	Term		Value
Outstanding at January 1, 2017	450	$	13.48
Granted	—		—
Exercised	—		—
Cancelled	—		—
Outstanding at December 31, 2017	450	$	13.48	5.45	$	2,774
Exercisable at December 31, 2017	250	$	13.48	5.45	$	1,541

Activity under the plans during 2016 was as follows:



				Weighted
			Weighted	Average
	Number of		Average	Remaining		Aggregate
	Shares		Exercise	Contractual		Intrinsic
Time-Based Stock Options	Outstanding		Price	Term		Value
Outstanding at January 1, 2016	2,734	$	11.75
Granted	215		16.74
Exercised	(394)		8.47
Cancelled	(101)		16.66
Outstanding at December 31, 2016	2,454	$	12.51	6.02	$	18,295
Vested and expected to vest	2,420	$	12.42	5.99	$	18,228
Exercisable at December 31, 2016	1,914	$	11.01	5.40	$	16,897


			Weighted
	Number of		Average
	Shares		Grant Date
Restricted Stock	Outstanding		Fair Value
Outstanding at January 1, 2016	1,071	$	17.30
Awarded	710		16.35
Forfeited	(70)		17.31
Released	(295)		14.49
Outstanding at December 31, 2016	1,416	$	17.40


				Weighted
			Weighted	Average
	Number of		Average	Remaining		Aggregate
	Shares		Exercise	Contractual		Intrinsic
Performance Stock Options	Outstanding		Price	Term		Value
Outstanding at January 1, 2016	450	$	13.48
Granted	—		—
Exercised	—		—
Cancelled	—		—
Outstanding at December 31, 2016	450	$	13.48	6.45	$	3,074
Exercisable at December 31, 2016	250	$	13.48	6.45	$	1,708

Share-Based Compensation Expense Related to Employee Share-Based Compensation



	2017		2016		2015
Cost of revenue	$	610	$	420	$	416
Research and development expenses		2,052		1,825		1,373
Selling, general and administrative expenses		11,953		9,452		7,208
Total	$	14,615	$	11,697	$	8,997

Assumptions Used for Determining Fair Value of Options



	2017		2016		2015
Risk-free interest rate	1.75 - 2.12	%	1.06 - 2.02	%	1.30 - 1.96	%
Expected life of option (years)	5.21 to 5.76		5.27 to 7.10		5.20 to 6.89
Expected volatility of stock	43.00 - 48.00	%	46.00 - 51.00	%	46.00 - 67.00	%
Weighted-average volatility	44.50	%	48.87	%	54.75	%
Dividend yield	0.00	%	0.00	%	0.00	%

Weighted Average Estimated Grant Date Fair Value Per Share of Stock Options and Restricted Stock Granted



	2017		2016		2015
Stock options	$	8.60	$	8.25	$	11.12
Restricted stock		19.38		16.35		17.82

Estimated Grant Date Fair Value Per Share of Performance Options Granted



	Price		Fair Value of		Fair Value of
	Target		2012 Grant		2014 Grant
Tranche 1	$	10.00	$	4.32	$	14.74
Tranche 2		12.50		4.30		14.74
Tranche 3		15.00		4.27		14.74
Tranche 4		17.50		4.23		14.74
Tranche 5		20.00		4.19		14.73
Tranche 6		25.00		4.10		14.73
Tranche 7		30.00		4.01		14.71
Tranche 8		35.00		3.92		14.67
Tranche 9		40.00		3.83		14.61

Segment and Geographic Information (Tables)

12 Months Ended

Dec. 31, 2017

Segment and Geographic Information [Abstract]

Revenue by Geographic Area



	2017		2016		2015
United States	$	138,387	$	122,385	$	102,212
Europe		21,901		19,772		17,180
Asia		13,616		12,223		9,510
Other international		812		729		853
Total international		36,329		32,724		27,543
Total revenue	$	174,716	$	155,109	$	129,755

Revenue by Product Type

United States revenue by product type was as follows:



	2017		2016		2015
Open-heart ablation	$	64,517	$	58,050	$	53,541
Minimally invasive ablation		34,421		31,169		21,564
AtriClip devices		37,281		30,321		24,377
Total ablation and AtriClip devices		136,219		119,540		99,482
Valve tools		2,168		2,845		2,730
Total United States	$	138,387	$	122,385	$	102,212

International revenue by product type was as follows:



	2017		2016		2015
Open-heart ablation	$	20,718	$	20,189	$	16,287
Minimally invasive ablation		8,007		8,065		7,964
AtriClip devices		7,251		3,986		2,868
Total ablation and AtriClip devices		35,976		32,240		27,119
Valve tools		353		484		424
Total international	$	36,329	$	32,724	$	27,543

Selected Quarterly Financial Data (Tables)

12 Months Ended

Dec. 31, 2017

Selected Quarterly Financial Data [Abstract]

Schedule of Quarterly Financial Information



	For the Three Months Ended
	March 31,				June 30,				September 30,				December 31,
	2017		2016		2017		2016		2017		2016		2017		2016
Operating Results:
Revenue	$	41,273	$	35,940	$	45,231	$	39,672	$	42,150	$	38,340	$	46,062	$	41,157
Gross profit		30,008		25,914		32,554		28,818		30,918		27,472		32,683		28,897
Loss from operations		(9,642)		(9,419)		(6,355)		(7,738)		(6,847)		(6,286)		(2,135)		(7,695)
Net loss		(10,183)		(9,724)		(6,883)		(8,206)		(7,246)		(6,783)		(2,580)		(8,625)
Net loss per share (basic and diluted)	$	(0.32)	$	(0.31)	$	(0.21)	$	(0.26)	$	(0.22)	$	(0.21)	$	(0.08)	$	(0.27)

Description of Business and Summary of Significant Accounting Policies (Narrative) (Details) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Description Of Business And Significant Accounting Policies [Line Items]
Shipping and handling revenue	$ 1,090	$ 1,266	$ 1,056
Payment terms for end-users	30 days
Payment terms for distributors	60 days
Depreciation	$ 7,761	7,655	4,975
Net carrying amount of loaned equipment	$ 28,749	$ 29,995
Company's expense related to the medical device excise tax			$ 667
Options, restricted stock and performance based shares excluded from calculation of net loss per share	4,321	4,320	4,255
Advertising costs	$ 900	$ 625	$ 476
Share-based compensation expense recognized	$ 14,615	$ 11,697	$ 8,997
Maximum [Member]
Description Of Business And Significant Accounting Policies [Line Items]
Maturity period of short term investment	1 year

Description of Business and Summary of Significant Accounting Policies (Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total accumulated other comprehensive loss at beginning of period	$ (468)	$ (611)	$ (348)
Total accumulated other comprehensive income (loss) at end of period	34	(468)	(611)
Unrealized Losses On Investments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total accumulated other comprehensive loss at beginning of period	(21)	(39)	(54)
Other comprehensive income before reclassifications	15	18	15
Amounts reclassified from accumulated other comprehensive income (loss) to other income (loss)
Total accumulated other comprehensive income (loss) at end of period	(6)	(21)	(39)
Foreign Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total accumulated other comprehensive loss at beginning of period	(447)	(572)	(294)
Other comprehensive income before reclassifications	660	532	156
Amounts reclassified from accumulated other comprehensive income (loss) to other income (loss)	(173)	(407)	(434)
Total accumulated other comprehensive income (loss) at end of period	$ 40	$ (447)	$ (572)

Fair Value (Narrative) (Details) $ in Thousands		12 Months Ended		48 Months Ended
Fair Value (Narrative) (Details) $ in Thousands	Oct. 13, 2015 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Change in value of contingent consideration		$ (4,078)	$ 969
Scenario, Forecast [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration revenue to target ratio				1.5
Payment of contingent consideration when commercial milestone achieved time allotment period				65 days
nContact Surgical [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Change in value of contingent consideration		4,078	$ 969
Fair value of AtriCure common stock issued at closing	$ 3,757	5,660
Patient Enrollment In Converge IDE Trial [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Change in value of contingent consideration		$ 7,500
Number of days payment due following enrollment		30 days
Completion Of CONVERGE IDE Trial And Receiving A PMA From FDA [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Potential contingent consideration reduction, percentage		8.33%
Potential contingent consideration reduction if regulatory milestone not met		$ 0
Number of days payment due following receipt of approval		30 days
Maximum [Member] \| Completion Of CONVERGE IDE Trial And Receiving A PMA From FDA [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Change in value of contingent consideration		$ 42,500

Fair Value (Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Assets:
Total assets	$ 26,165	$ 39,886
Liabilities:
Acquisition-related contingent consideration	37,098	41,176
Total liabilities	37,098	41,176
Money Market Funds [Member]
Assets:
Total assets	12,774	17,085
Commercial Paper [Member]
Assets:
Total assets	7,472	5,996
U.S. Government Agencies and Securities [Member]
Assets:
Total assets	2,999	8,529
Corporate Bonds [Member]
Assets:
Total assets	2,920	8,276
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets:
Total assets	2,999	7,000
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| U.S. Government Agencies and Securities [Member]
Assets:
Total assets	2,999	7,000
Significant Other Observable Inputs (Level 2) [Member]
Assets:
Total assets	23,166	32,886
Significant Other Observable Inputs (Level 2) [Member] \| Money Market Funds [Member]
Assets:
Total assets	12,774	17,085
Significant Other Observable Inputs (Level 2) [Member] \| Commercial Paper [Member]
Assets:
Total assets	7,472	5,996
Significant Other Observable Inputs (Level 2) [Member] \| U.S. Government Agencies and Securities [Member]
Assets:
Total assets		1,529
Significant Other Observable Inputs (Level 2) [Member] \| Corporate Bonds [Member]
Assets:
Total assets	2,920	8,276
Significant Other Unobservable Inputs (Level 3) [Member]
Liabilities:
Acquisition-related contingent consideration	37,098	41,176
Total liabilities	$ 37,098	$ 41,176

Fair Value (Level 3 Fair Value Measurements Using Significant Other Unobservable Inputs for Derivative Instruments) (Details) - Significant Other Unobservable Inputs (Level 3) [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance – January 1			$ 120
Total (gains) losses included in earnings			57
Exercises			(177)
Ending Balance – December 31

Fair Value (Level 3 Fair Value Measurements Using Significant Other Unobservable Inputs for Acquisition-Related Contingent Consideration) (Details) - Significant Other Unobservable Inputs (Level 3) [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 41,176	$ 40,207
Amounts acquired			40,207
Changes in fair value included in earnings	(4,078)	969
Ending Balance	$ 37,098	$ 41,176	$ 40,207

Investments (Narrative) (Details)	12 Months Ended
Investments (Narrative) (Details)	Dec. 31, 2016
Minimum [Member]
Investment [Line Items]
Long term marketable debt securities maturity period	1 year
Maximum [Member]
Investment [Line Items]
Long term marketable debt securities maturity period	2 years

Investments (Summary Of Short-term Investments) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Investment [Line Items]
Short-term investments, Cost Basis	$ 12,648	$ 22,822
Short-term investment, Unrealized gains (losses)	(6)	(21)
Short-term investments, Fair value	12,642	22,801
Corporate Bonds [Member]
Investment [Line Items]
Short-term investments, Cost Basis	2,925	8,284
Short-term investment, Unrealized gains (losses)	(5)	(8)
Short-term investments, Fair value	2,920	8,276
U.S. Government Agencies and Securities [Member]
Investment [Line Items]
Short-term investments, Cost Basis	3,000	8,542
Short-term investment, Unrealized gains (losses)	(1)	(13)
Short-term investments, Fair value	2,999	8,529
Commercial Paper [Member]
Investment [Line Items]
Short-term investments, Cost Basis	6,723	5,996
Short-term investments, Fair value	$ 6,723	$ 5,996

Intangible Assets and Goodwill (Narative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Intangible Assets and Goodwill [Abstract]
Amortization of intangible assets	$ 1,367	$ 1,644	$ 1,303

Intangible Assets and Goodwill (Company's Intangible Assets) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Cost	$ 56,271	$ 56,271
Accumulated Amortization	$ 5,507	4,140
Fusion Technology [Member]
Finite-Lived Intangible Assets [Line Items]
Estimated Useful Life	10 years
Cost	$ 9,242	9,242
Accumulated Amortization	$ 3,697	2,773
Clamp and Probe Technology [Member]
Finite-Lived Intangible Assets [Line Items]
Estimated Useful Life	3 years
Cost	$ 829	829
Accumulated Amortization	$ 829	829
SUBTLE Access Technology [Member]
Finite-Lived Intangible Assets [Line Items]
Estimated Useful Life	5 years
Cost	$ 2,179	2,179
Accumulated Amortization	981	538
IPR&D [Member]
Finite-Lived Intangible Assets [Line Items]
Cost	$ 44,021	$ 44,021

Intangible Assets and Goodwill (Future Amortization Expense Related to Intangible Assets with Definite Lives) (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Intangible Assets and Goodwill [Abstract]
2018	$ 1,367
2019	1,367
2020	1,235
2021	924
2022	925
2023 and thereafter	925
Total	$ 6,743

Intangible Assets and Goodwill (Summary Of Company's Goodwill) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Intangible Assets and Goodwill [Abstract]
Goodwill, Beginning Balance	$ 105,257	$ 105,257
Additions (Impairments)
Goodwill, Ending Balance	$ 105,257	$ 105,257

Inventories (Summary Of Inventories) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Inventories [Abstract]
Raw materials	$ 7,755	$ 5,719
Work in process	1,299	1,221
Finished goods	13,397	10,720
Inventories	$ 22,451	$ 17,660

Property and Equipment (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Depreciation	$ 7,761	$ 7,655	$ 4,975
Net carrying amount of loaned equipment	28,749	29,995
Generators and Other Capital Equipment [Member]
Property, Plant and Equipment [Line Items]
Depreciation	3,574	3,591	$ 2,944
Net carrying amount of loaned equipment	$ 4,656	$ 5,692

Property and Equipment (Summary Of Property And Equipment) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 50,486	$ 44,138
Less accumulated depreciation	(21,737)	(14,143)
Property, and equipment, net	28,749	29,995
Generators and Other Capital Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	15,754	13,087
Property, and equipment, net	$ 4,656	5,692
Building under Capital Lease [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	15 years
Property and equipment, gross	$ 14,250	14,250
Computer and Other Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	3 years
Property and equipment, gross	$ 5,873	5,321
Machinery, Equipment and Vehicles [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	4,576	3,731
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	4,366	3,676
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	3,636	3,319
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	1,810	539
Equipment under Capital Leases [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 221	$ 215
Minimum [Member] \| Generators and Other Capital Equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	1 year
Minimum [Member] \| Machinery, Equipment and Vehicles [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	3 years
Minimum [Member] \| Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	3 years
Minimum [Member] \| Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	5 years
Minimum [Member] \| Equipment under Capital Leases [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	3 years
Maximum [Member] \| Generators and Other Capital Equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	3 years
Maximum [Member] \| Machinery, Equipment and Vehicles [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	7 years
Maximum [Member] \| Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	7 years
Maximum [Member] \| Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	15 years
Maximum [Member] \| Equipment under Capital Leases [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	5 years

Accrued Liabilities (Accrued Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accrued Liabilities [Abstract]
Accrued commissions	$ 6,964	$ 5,737
Accrued bonus	4,726	2,871
Accrued payroll and employee-related expenses	4,097	4,326
Sales returns and allowances	1,169	834
Other accrued liabilities	695	929
Accrued taxes and value-added taxes payable	634	1,289
Accrued royalties	626	481
Total	$ 18,911	$ 16,467

Indebtedness (Narrative) (Details) - USD ($)			12 Months Ended
Indebtedness (Narrative) (Details) - USD ($)	Feb. 23, 2018	Apr. 25, 2016	Dec. 31, 2017
Line of Credit Facility [Line Items]
Cost of assets under lease			$ 14,471,000
Accumulated amortization on the capital leases			$ 2,249,000
Maximum [Member]
Line of Credit Facility [Line Items]
Loan term			1 year
Silicon Valley Bank Agreement [Member] \| Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of credit			$ 15,000,000
Line of credit, amount outstanding			0
Line of credit, availability			$ 15,000,000
Silicon Valley Bank, Second Amended And Restated Loan Agreement [Member]
Line of Credit Facility [Line Items]
Principal payment starting period after inception of loan to maturity		18 months
Silicon Valley Bank, Second Amended And Restated Loan Agreement [Member] \| Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Maturity date			Apr. 30, 2021
Annual commitment fee		$ 50,000
Silicon Valley Bank, Second Amended And Restated Loan Agreement [Member] \| Revolving Credit Facility [Member] \| Subsequent Event [Member]
Line of Credit Facility [Line Items]
Additional fee on total term loan	0.33%
Silicon Valley Bank, Third Amended And Restated Loan Agreement [Member] \| Subsequent Event [Member]
Line of Credit Facility [Line Items]
Principal payment starting period after inception of loan to maturity	18 months
Upon certain conditions met, deferred loan payment period	6 months
Silicon Valley Bank, Third Amended And Restated Loan Agreement [Member] \| Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Maturity date			Feb. 28, 2023
Silicon Valley Bank, Third Amended And Restated Loan Agreement [Member] \| Revolving Credit Facility [Member] \| Subsequent Event [Member]
Line of Credit Facility [Line Items]
Line of credit, maximum borrowing capacity	$ 20,000,000
Credit facility, expiration period	5 years
Optional increase in line of credit	$ 20,000,000
Computer And Office Equipment [Member]
Line of Credit Facility [Line Items]
Capital lease expiration period			Dec. 31, 2030
Term Loan [Member] \| Silicon Valley Bank, Second Amended And Restated Loan Agreement [Member]
Line of Credit Facility [Line Items]
Loan amount		$ 25,000,000
Loan term		5 years
Additional fee on total term loan		4.00%
Accrued fee amount			$ 337,000
Term Loan [Member] \| Silicon Valley Bank, Second Amended And Restated Loan Agreement [Member] \| Subsequent Event [Member]
Line of Credit Facility [Line Items]
Additional fee on total term loan	3.50%
Term Loan [Member] \| Silicon Valley Bank, Third Amended And Restated Loan Agreement [Member] \| Subsequent Event [Member]
Line of Credit Facility [Line Items]
Loan amount	$ 40,000,000
Term Loan [Member] \| Silicon Valley Bank, Third Amended And Restated Loan Agreement [Member] \| Prime Rate [Member] \| Subsequent Event [Member]
Line of Credit Facility [Line Items]
Basis rate	3.75%
Interest rate	8.25%
Mason Lease [Member] \| Letter of Credit [Member]
Line of Credit Facility [Line Items]
Letter of credit outstanding			$ 1,250,000

Indebtedness (Future Maturities On Debt And Capital Lease Obligations) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Indebtedness [Abstract]
2018	$ 1,468
2019	3,755
2020	8,305
2021	8,309
2022	8,335
2023 and thereafter	14,379
Total payments	44,551
Imputed interest	(7,129)
Net long-term debt and capital lease obligations, of which $561 is current and $36,861 is noncurrent	37,422
Net capital lease obligations, current	561	$ 1,688
Net capital lease obligations, noncurrent	$ 36,861

Commitments and Contingencies (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Commitments and Contingencies [Line Items]
Operating lease rent expense	$ 850	$ 1,250	$ 1,515
Royalty expense	$ 2,323	$ 1,895	$ 1,799
Minimum [Member]
Commitments and Contingencies [Line Items]
Royalty rates	3.00%
Maximum [Member]
Commitments and Contingencies [Line Items]
Royalty rates	5.00%
Royalty agreement term	20 years
Office, Manufacturing, Warehouse Facilities, And Equipment [Member]
Commitments and Contingencies [Line Items]
Operating leases expire at various terms	Dec. 31, 2022

Commitments and Contingencies (Future Minimum Lease Payments Under Non-cancelable Operating Leases) (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Commitments and Contingencies [Abstract]
2018	$ 965
2019	927
2020	737
2021	413
2022	306
Total	$ 3,348

Income Taxes (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
Income Taxes (Narrative) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Contingency [Line Items]
Federal tax at statutory rate		34.00%	34.00%	34.00%
Reduction to federal deferred tax assets		$ 29,480
Corporate alternative minimum tax, deferred tax benefit		102
Research and development credit carryforward		5,339	$ 5,446
Pre-tax book loss for domestic operations		(19,409)	(27,271)	$ (21,157)
Pre-tax book loss for international operations		(7,469)	(6,027)	(6,019)
Undistributed earnings of foreign subsidiaries		107
Unrecognized deferred tax assets		2,816	2,816
Deferred tax assets tax credit carryforwards research and unrecognized tax benefits reduction from IRS audit		2,018
Unrecognized tax benefits that would impact effective tax rate		0	0	0
Unrecognized tax benefits		1,157	$ 3,175	$ 1,982	$ 1,982
Scenario, Plan [Member]
Income Tax Contingency [Line Items]
Federal tax at statutory rate	21.00%
Federal [Member]
Income Tax Contingency [Line Items]
Operating loss carryforward		240,286
Research and development credit carryforward		6,392
State [Member]
Income Tax Contingency [Line Items]
Operating loss carryforward		147,841
Foreign [Member]
Income Tax Contingency [Line Items]
Operating loss carryforward		$ 30,501
Minimum [Member] \| Federal [Member]
Income Tax Contingency [Line Items]
Operating loss carryforward, expiration year		Dec. 31, 2021
Research and development credit credit carryforwards expiration year		Dec. 31, 2022
Minimum [Member] \| State [Member]
Income Tax Contingency [Line Items]
Operating loss carryforward, expiration year		Dec. 31, 2018
Minimum [Member] \| Foreign [Member]
Income Tax Contingency [Line Items]
Operating loss carryforward, expiration year		Dec. 31, 2018
Maximum [Member] \| Federal [Member]
Income Tax Contingency [Line Items]
Operating loss carryforward, expiration year		Dec. 31, 2038
Research and development credit credit carryforwards expiration year		Dec. 31, 2038
Maximum [Member] \| State [Member]
Income Tax Contingency [Line Items]
Operating loss carryforward, expiration year		Dec. 31, 2038
Maximum [Member] \| Foreign [Member]
Income Tax Contingency [Line Items]
Operating loss carryforward, expiration year		Dec. 31, 2027

Income Taxes (Summary Of Detail Of Deferred Tax Assets And Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets (liabilities):
Net operating loss carryforward	$ 64,776	$ 84,056
Research and development and AMT credit carryforwards, net	5,339	5,446
Equity compensation	6,955	8,406
Accruals and reserves	874	914
Inventories	588	1,503
Intangible assets	(11,297)	(16,922)
Property and equipment, net	(339)	(1,487)
Other, net	179	66
Subtotal	67,075	81,982
Less valuation allowance	(66,973)	(81,982)
Total	$ 102

Income Taxes (Summary Of Company's Provision for Income Taxes) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current Tax Expense
Federal			$ 2
State	$ 44	$ 32	34
Foreign	72	8
Total current tax expense	116	40	36
Deferred Tax Expense
Federal	18,485	(7,333)	(7,154)
State	(1,337)	210	(398)
Foreign	(2,241)	(1,177)	(955)
Change in valuation allowance	(15,009)	8,300	8,507
Total deferred tax expense	(102)
Total tax expense	$ 14	$ 40	$ 36

Income Taxes (Summary Of Difference Between Effective Income Tax Rates And Federal Statutory Rate) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes [Abstract]
Federal tax at statutory rate	34.00%	34.00%	34.00%
Federal tax rate change	(109.68%)
Federal R&D credit	(0.40%)	2.89%	3.23%
Federal NOL adjustment for ASU	10.48%
Valuation allowance	55.84%	(24.93%)	(31.30%)
State income taxes	4.81%	(0.69%)	1.38%
Foreign NOL rate change	1.30%	(1.36%)	(2.02%)
Foreign tax rate differential	(2.45%)	(1.62%)	(1.99%)
Permanent differences and other	6.05%	(8.41%)	(3.43%)
Effective tax rate, Total	(0.05%)	(0.12%)	(0.13%)
Federal tax at statutory rate	$ (9,139)	$ (11,322)	$ (9,240)
Federal tax rate change	29,480
Federal R&D credit	107	(962)	(878)
Federal NOL adjustment for ASU	(2,816)
Valuation allowance	(15,009)	8,300	8,507
State income taxes	(1,292)	231	(375)
Foreign NOL rate change	(348)	452	549
Foreign tax rate differential	658	539	542
Permanent differences and other	(1,627)	2,802	931
Total tax expense	$ 14	$ 40	$ 36

Income Taxes (Summary Of Reconciliation Of Change In Federal And State Unrecognized Tax Benefits) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes [Abstract]
Balance at the beginning of the year	$ 3,175	$ 1,982	$ 1,982
Increases (decreases) for prior year tax positions		1,193
Increases (decreases) for prior year tax positions	(2,018)
Increases (decreases) for current year tax positions
Increases (decreases) related to settlements
Decreases related to statute lapse
Balance at the end of the year	$ 1,157	$ 3,175	$ 1,982

Concentrations (Narrative) (Details) $ in Thousands	12 Months Ended
Concentrations (Narrative) (Details) $ in Thousands	Dec. 31, 2017 USD ($) customer	Dec. 31, 2016	Dec. 31, 2015
Concentration Risk [Line Items]
Number of customers \| customer	10
Cash and cash equivalents balance in excess of FDIC limits \| $	$ 21,360
Net Revenue [Member]
Concentration Risk [Line Items]
Percentage representation of significant customer	13.20%	14.40%	12.90%
Customer Concentration Risk [Member] \| Net Revenue [Member]
Concentration Risk [Line Items]
Percentage representation of significant customer	10.00%
Customer Concentration Risk [Member] \| Accounts Receivable [Member]
Concentration Risk [Line Items]
Percentage representation of significant customer	19.70%	19.90%

Employee Benefit Plans (Narrative) (Details) - USD ($)	12 Months Ended
Employee Benefit Plans (Narrative) (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employee Benefit Plans [Abstract]
Employee contribution percent	50.00%	50.00%	50.00%
Maximum percentage of employee contribution to the plan	6.00%	6.00%	6.00%
Company's matching contribution	$ 1,367,000	$ 1,222,000	$ 1,007,000
Discretionary contributions made	0	0	0
Total contributions to retirement plan	$ 205,000	$ 101,000	$ 133,000

Equity Compensation Plans (Narrative) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	1 Months Ended	12 Months Ended
	Jan. 31, 2014	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total intrinsic value of options exercised		$ 5,121	$ 3,550	$ 2,740
Tax benefit recognized		0	0	0
Share-based compensation expense recognized		14,615	11,697	8,997
Unrecognized compensation costs related to non-vested share-based compensation arrangements with performance shares		23,331
Share-based compensation expense		$ 14,615	11,697	8,997
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average period of recognizing cost		2 years 2 months 12 days
Stock options compensation costs		$ 2,197
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average period of recognizing cost		2 years 2 months 12 days
Total fair value of restricted stock vested		$ 6,235	$ 5,102	2,767
Unrecognized compensation costs related to non-vested performance options		$ 21,134
Performance options awarded to President and CEO		771	710
Performance Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiry of options from the date of grant		10 years
Share-based compensation expense		$ 43	$ 269	546
Performance options awarded to President and CEO	450
Number of shares options vest in		25
Period of considering closing price of common stock		30 days
Contractual term (years)		10 years
Stock Options And Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense recognized		$ 13,908	$ 10,872	$ 8,072
Minimum [Member] \| Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Contractual term (years)		5 years 2 months 16 days	5 years 3 months 7 days	5 years 2 months 12 days
Expected volatility of stock		43.00%	46.00%	46.00%
Interest rate		1.75%	1.06%	1.30%
Minimum [Member] \| Performance Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Strike price		$ 5.91
Expected volatility of stock		60.50%
Interest rate		1.75%
Maximum [Member] \| Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Contractual term (years)		5 years 9 months 4 days	7 years 1 month 6 days	6 years 10 months 21 days
Expected volatility of stock		48.00%	51.00%	67.00%
Interest rate		2.12%	2.02%	1.96%
Maximum [Member] \| Performance Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Strike price		$ 21.04
Expected volatility of stock		69.60%
Interest rate		2.73%
2014 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiry of options from the date of grant		10 years
Common stock reserved for issuance		10,249
Shares available for future grants		1,128
2014 Plan [Member] \| Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercisable period beginning		3 years
2014 Plan [Member] \| Minimum [Member] \| Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		1 year
2014 Plan [Member] \| Maximum [Member] \| Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		4 years
2008 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense recognized		$ 664	$ 556	$ 379
Company's common stock may be purchased at a discount		15.00%
Participants purchase limit value		$ 25
Description of participants purchase limit		Participants may not purchase more than $25 of the Company's common stock in a calendar year and may not purchase a value of more than 3 shares during an offering period.
Participants purchase limit shares		3
Offering period		6 months
Shares available for sale under the ESPP increased		2.00%
Outstanding shares of common stock exceed		600
Shares available for future issuance under the ESPP		225
First Anniversary Date Of Grant [Member] \| 2014 Plan [Member] \| Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual vesting percentage		25.00%
Tranche 4 [Member] \| Performance Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Price by which volume adjusted weighted average closing price exceeds under vesting condition		$ 17.50
Tranche 5 [Member] \| Performance Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Price by which volume adjusted weighted average closing price exceeds under vesting condition		20.00
Tranche 6 [Member] \| Performance Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Price by which volume adjusted weighted average closing price exceeds under vesting condition		25.00
Tranche 7 [Member] \| Performance Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Price by which volume adjusted weighted average closing price exceeds under vesting condition		30.00
Tranche 8 [Member] \| Performance Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Price by which volume adjusted weighted average closing price exceeds under vesting condition		35.00
Tranche 9 [Member] \| Performance Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Price by which volume adjusted weighted average closing price exceeds under vesting condition		$ 40.00

Equity Compensation Plans (Activity Under Stock Based Compensation Plans) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	1 Months Ended	12 Months Ended
	Jan. 31, 2014	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning balance, Number of Shares Outstanding, Stock Options		2,454	2,734
Granted, Number of Shares Outstanding, Stock Options		65	215
Exercised, Number of Shares Outstanding, Stock Options		(458)	(101)
Cancelled or forfeited, Number of Shares Outstanding, Stock Options		(35)	(394)
Ending balance, Number of Shares Outstanding, Stock Options		2,026	2,454	2,734
Vested and expected to vest, Number of Shares Outstanding, Stock Options		2,004	2,420
Exercisable, Ending balance, Number of Shares Outstanding, Stock Options		1,766	1,914
Beginning balance, Weighted Average Exercise Price, Stock Options		$ 12.51	$ 11.75
Granted, Weighted Average Exercise Price, Stock Options		20.22	16.74
Exercised, Weighted Average Exercise Price, Stock Options		9.61	16.66
Cancelled or forfeited, Weighted Average Exercise Price, Stock Options		19.08	8.47
Ending balance, Weighted Average Exercise Price, Stock Options		13.30	12.51	$ 11.75
Vested and expected to vest, Weighted Average Exercise Price, Stock Options		13.23	12.42
Exercisable, Ending balance, Weighted Average Exercise Price, Stock Options		$ 12.48	$ 11.01
Outstanding, Ending balance, Weighted Average Remaining Contractual Term, Stock Options		5 years 7 months 13 days	6 years 7 days
Vested and expected to vest, Weighted Average Remaining Contractual Term, Stock Options		5 years 6 months 29 days	5 years 11 months 27 days
Exercisable, Ending balance, Weighted Average Remaining Contractual Term, Stock Options		5 years 2 months 12 days	5 years 4 months 24 days
Outstanding, Ending balance, Aggregate Intrinsic Value, Stock Options		$ 11,730	$ 18,295
Vested and expected to vest, Aggregate Intrinsic Value, Stock Options		11,717	18,228
Exercisable, Ending balance, Aggregate Intrinsic Value, Stock Options		$ 11,471	$ 16,897
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning balance, Number of Shares Outstanding		1,416	1,071
Awarded, Number of Shares Outstanding		771	710
Released, Number of Shares Outstanding		(331)	(295)
Forfeited, Number of Shares Outstanding		(11)	(70)
Ending balance, Number of Shares Outstanding		1,845	1,416	1,071
Beginning balance, Weighted Average Grant Date Fair Value		$ 17.40	$ 17.30
Awarded, Weighted Average Grant Date Fair Value		19.38	16.35	$ 17.82
Released, Weighted Average Grant Date Fair Value		17.43	14.49
Forfeited, Weighted Average Grant Date Fair Value		18.52	17.31
Ending balance, Weighted Average Grant Date Fair Value		$ 18.22	$ 17.40	$ 17.30
Performance Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning balance, Number of Shares Outstanding, Stock Options		450	450
Granted, Number of Shares Outstanding, Stock Options
Exercised, Number of Shares Outstanding, Stock Options
Cancelled or forfeited, Number of Shares Outstanding, Stock Options
Ending balance, Number of Shares Outstanding, Stock Options		450	450	450
Exercisable, Ending balance, Number of Shares Outstanding, Stock Options		250	250
Awarded, Number of Shares Outstanding	450
Beginning balance, Weighted Average Exercise Price, Stock Options		$ 13.48	$ 13.48
Granted, Weighted Average Exercise Price, Stock Options
Exercised, Weighted Average Exercise Price, Stock Options
Cancelled or forfeited, Weighted Average Exercise Price, Stock Options
Ending balance, Weighted Average Exercise Price, Stock Options		13.48	13.48	$ 13.48
Exercisable, Ending balance, Weighted Average Exercise Price, Stock Options		$ 13.48	$ 13.48
Outstanding, Ending balance, Weighted Average Remaining Contractual Term, Stock Options		5 years 5 months 12 days	6 years 5 months 12 days
Exercisable, Ending balance, Weighted Average Remaining Contractual Term, Stock Options		5 years 5 months 12 days	6 years 5 months 12 days
Outstanding, Ending balance, Aggregate Intrinsic Value, Stock Options		$ 2,774	$ 3,074
Exercisable, Ending balance, Aggregate Intrinsic Value, Stock Options		$ 1,541	$ 1,708

Equity Compensation Plans (Share-Based Compensation Expense Related to Employee Share-Based Compensation) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total	$ 14,615	$ 11,697	$ 8,997
Cost of Revenue [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total	610	420	416
Research and Development Expenses [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total	2,052	1,825	1,373
Selling, General and Administrative Expenses [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total	$ 11,953	$ 9,452	$ 7,208

Equity Compensation Plans (Assumptions Used for Determining Fair Value of Options) (Details) - Employee Stock Option [Member]	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average volatility	44.50%	48.87%	54.75%
Dividend yield	0.00%	0.00%	0.00%
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	1.75%	1.06%	1.30%
Expected life of option (years)	5 years 2 months 16 days	5 years 3 months 7 days	5 years 2 months 12 days
Expected volatility of stock	43.00%	46.00%	46.00%
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	2.12%	2.02%	1.96%
Expected life of option (years)	5 years 9 months 4 days	7 years 1 month 6 days	6 years 10 months 21 days
Expected volatility of stock	48.00%	51.00%	67.00%

Equity Compensation Plans (Weighted Average Estimated Grant Date Fair Value Per Share of Stock Options and Restricted Stock Granted) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average estimated grant date fair value per share of the stock options granted	$ 8.60	$ 8.25	$ 11.12
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average estimated grant date fair value per share of the restricted stock granted	$ 19.38	$ 16.35	$ 17.82

Segment and Geographic Information (Narrative)(Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Europe [Member]
Long-lived assets	$ 957	$ 931

Segment and Geographic Information (Revenue by Geographic Area) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	$ 46,062	$ 42,150	$ 45,231	$ 41,273	$ 41,157	$ 38,340	$ 39,672	$ 35,940	$ 174,716	$ 155,109	$ 129,755
United States [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									138,387	122,385	102,212
Europe [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									21,901	19,772	17,180
Asia [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									13,616	12,223	9,510
Other International [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									812	729	853
International [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									$ 36,329	$ 32,724	$ 27,543

Segment and Geographic Information (Revenue by Product Type) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue from External Customer [Line Items]
Revenue	$ 46,062	$ 42,150	$ 45,231	$ 41,273	$ 41,157	$ 38,340	$ 39,672	$ 35,940	$ 174,716	$ 155,109	$ 129,755
United States [Member]
Revenue from External Customer [Line Items]
Revenue									138,387	122,385	102,212
United States [Member] \| Open-heart Ablation [Member]
Revenue from External Customer [Line Items]
Revenue									64,517	58,050	53,541
United States [Member] \| Minimally Invasive Ablation [Member]
Revenue from External Customer [Line Items]
Revenue									34,421	31,169	21,564
United States [Member] \| AtriClip Devices [Member]
Revenue from External Customer [Line Items]
Revenue									37,281	30,321	24,377
United States [Member] \| Ablation and AtriClip Devices [Member]
Revenue from External Customer [Line Items]
Revenue									136,219	119,540	99,482
United States [Member] \| Valve Tools [Member]
Revenue from External Customer [Line Items]
Revenue									2,168	2,845	2,730
International [Member]
Revenue from External Customer [Line Items]
Revenue									36,329	32,724	27,543
International [Member] \| Open-heart Ablation [Member]
Revenue from External Customer [Line Items]
Revenue									20,718	20,189	16,287
International [Member] \| Minimally Invasive Ablation [Member]
Revenue from External Customer [Line Items]
Revenue									8,007	8,065	7,964
International [Member] \| AtriClip Devices [Member]
Revenue from External Customer [Line Items]
Revenue									7,251	3,986	2,868
International [Member] \| Ablation and AtriClip Devices [Member]
Revenue from External Customer [Line Items]
Revenue									35,976	32,240	27,119
International [Member] \| Valve Tools [Member]
Revenue from External Customer [Line Items]
Revenue									$ 353	$ 484	$ 424

Selected Quarterly Financial Data (Schedule Of Quarterly Financial Information) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Results:
Revenue	$ 46,062	$ 42,150	$ 45,231	$ 41,273	$ 41,157	$ 38,340	$ 39,672	$ 35,940	$ 174,716	$ 155,109	$ 129,755
Gross profit	32,683	30,918	32,554	30,008	28,897	27,472	28,818	25,914	126,163	111,101	92,875
Loss from operations	(2,135)	(6,847)	(6,355)	(9,642)	(7,695)	(6,286)	(7,738)	(9,419)	(24,979)	(31,138)	(26,720)
Net loss	$ (2,580)	$ (7,246)	$ (6,883)	$ (10,183)	$ (8,625)	$ (6,783)	$ (8,206)	$ (9,724)	$ (26,892)	$ (33,338)	$ (27,212)
Net loss per share (basic and diluted)	$ (0.08)	$ (0.22)	$ (0.21)	$ (0.32)	$ (0.27)	$ (0.21)	$ (0.26)	$ (0.31)

Schedule II (Schedule Of Valuation And Qualifying Accounts) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reserve For Sales Returns And Allowances [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	$ 834	$ 207	$ 135
Additions	441	634	78
Deductions	106	7	6
Ending Balance	1,169	834	207
Allowance For Inventory Valuation [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	1,080	843	522
Additions	1,004	1,692	720
Deductions	1,195	1,455	399
Ending Balance	889	1,080	843
Valuation Allowance For Deferred Tax Assets [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	81,982	73,682	59,554
Additions		8,300	14,128
Deductions	15,009
Ending Balance	$ 66,973	$ 81,982	$ 73,682

Equity Compensation Plans (Estimated Grant Date Fair Value Per Share of Performance Options Granted) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Fair Value	$ 8.60	$ 8.25	$ 11.12
Performance Stock Options [Member] \| Tranche 1 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Price Target	10.00
Performance Stock Options [Member] \| Tranche 2 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Price Target	12.50
Performance Stock Options [Member] \| Tranche 3 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Price Target	15.00
Performance Stock Options [Member] \| Tranche 4 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Price Target	17.50
Performance Stock Options [Member] \| Tranche 5 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Price Target	20.00
Performance Stock Options [Member] \| Tranche 6 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Price Target	25.00
Performance Stock Options [Member] \| Tranche 7 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Price Target	30.00
Performance Stock Options [Member] \| Tranche 8 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Price Target	35.00
Performance Stock Options [Member] \| Tranche 9 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Price Target	40.00
Fair Value Of 2012 Grant [Member] \| Performance Stock Options [Member] \| Tranche 1 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Fair Value	4.32
Fair Value Of 2012 Grant [Member] \| Performance Stock Options [Member] \| Tranche 2 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Fair Value	4.30
Fair Value Of 2012 Grant [Member] \| Performance Stock Options [Member] \| Tranche 3 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Fair Value	4.27
Fair Value Of 2012 Grant [Member] \| Performance Stock Options [Member] \| Tranche 4 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Fair Value	4.23
Fair Value Of 2012 Grant [Member] \| Performance Stock Options [Member] \| Tranche 5 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Fair Value	4.19
Fair Value Of 2012 Grant [Member] \| Performance Stock Options [Member] \| Tranche 6 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Fair Value	4.10
Fair Value Of 2012 Grant [Member] \| Performance Stock Options [Member] \| Tranche 7 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Fair Value	4.01
Fair Value Of 2012 Grant [Member] \| Performance Stock Options [Member] \| Tranche 8 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Fair Value	3.92
Fair Value Of 2012 Grant [Member] \| Performance Stock Options [Member] \| Tranche 9 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Fair Value	3.83
Fair Value Of 2014 Grant [Member] \| Performance Stock Options [Member] \| Tranche 1 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Fair Value	14.74
Fair Value Of 2014 Grant [Member] \| Performance Stock Options [Member] \| Tranche 2 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Fair Value	14.74
Fair Value Of 2014 Grant [Member] \| Performance Stock Options [Member] \| Tranche 3 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Fair Value	14.74
Fair Value Of 2014 Grant [Member] \| Performance Stock Options [Member] \| Tranche 4 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Fair Value	14.74
Fair Value Of 2014 Grant [Member] \| Performance Stock Options [Member] \| Tranche 5 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Fair Value	14.73
Fair Value Of 2014 Grant [Member] \| Performance Stock Options [Member] \| Tranche 6 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Fair Value	14.73
Fair Value Of 2014 Grant [Member] \| Performance Stock Options [Member] \| Tranche 7 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Fair Value	14.71
Fair Value Of 2014 Grant [Member] \| Performance Stock Options [Member] \| Tranche 8 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Fair Value	14.67
Fair Value Of 2014 Grant [Member] \| Performance Stock Options [Member] \| Tranche 9 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Fair Value	$ 14.61