AtriCure (ATRC) 10-K 1 Mar 19 2018 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Feb. 22, 2019	Jun. 30, 2018
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	FY
Trading Symbol	ATRC
Entity Registrant Name	AtriCure, Inc.
Entity Central Index Key	1,323,885
Current Fiscal Year End Date	--12-31
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Filer Category	Large Accelerated Filer
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Common Stock, Shares Outstanding		38,605,737
Entity Public Float			$ 911.1

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 32,231	$ 21,809
Short-term investments	92,171	12,642
Accounts receivable, less allowance for doubtful accounts of $547 and $32	25,195	23,083
Inventories	22,484	22,451
Prepaid and other current assets	2,592	2,273
Total current assets	174,673	82,258
Property and equipment, net	27,080	28,749
Intangible assets, net	49,254	50,764
Goodwill	105,257	105,257
Other noncurrent assets	495	676
Total Assets	356,759	267,704
Current liabilities:
Accounts payable	9,659	12,431
Accrued liabilities	25,840	18,911
Other current liabilities and current maturities of capital leases and long-term debt	4,717	561
Total current liabilities	40,216	31,903
Capital leases	12,172	12,761
Long-term debt	35,571	24,100
Other noncurrent liabilities	19,419	37,774
Total Liabilities	107,378	106,538
Commitments and contingencies (Note 7)
Stockholders' Equity:
Common stock, $0.001 par value, 90,000 shares authorized and 38,604 and 34,586 issued and outstanding	39	35
Additional paid-in capital	496,544	386,963
Accumulated other comprehensive (loss) income	(199)	34
Accumulated deficit	(247,003)	(225,866)
Total Stockholders' Equity	249,381	161,166
Total Liabilities and Stockholders' Equity	$ 356,759	$ 267,704

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Condensed Consolidated Balance Sheets [Abstract]
Accounts receivable, allowance for doubtful accounts	$ 547	$ 32
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	90,000,000	90,000,000
Common stock, shares issued	38,604,000	34,586,000
Common stock, shares outstanding	38,604,000	34,586,000

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Consolidated Statements of Operations and Comprehensive Loss [Abstract]
Revenue	$ 201,630	$ 174,716	$ 155,109
Cost of revenue	54,510	48,553	44,008
Gross profit	147,120	126,163	111,101
Operating expenses:
Research and development expenses	34,723	34,144	35,824
Selling, general and administrative expenses	129,524	116,998	106,415
Total operating expenses	164,247	151,142	142,239
Loss from operations	(17,127)	(24,979)	(31,138)
Other income (expense):
Interest expense	(4,607)	(2,264)	(1,801)
Interest income	1,006	227	227
Other	(183)	138	(586)
Loss before income tax expense	(20,911)	(26,878)	(33,298)
Income tax expense	226	14	40
Net loss	$ (21,137)	$ (26,892)	$ (33,338)
Basic and diluted net loss per share	$ (0.62)	$ (0.83)	$ (1.05)
Weighted average shares outstanding — basic and diluted	34,087	32,387	31,609
Comprehensive loss:
Unrealized (loss) gain on investments	$ (31)	$ 15	$ 18
Foreign currency translation adjustment	(202)	487	125
Other comprehensive (loss) income	(233)	502	143
Net loss	(21,137)	(26,892)	(33,338)
Comprehensive loss, net of tax	$ (21,370)	$ (26,390)	$ (33,195)

Consolidated Statements of Stoc

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, 2015	$ 32	$ 352,900	$ (165,636)	$ (611)	$ 186,685
Beginning 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 income (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 income (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
Issuance of common stock through public offering	$ 3	82,870			82,873
Issuance of common stock through public offering, Shares	2,875
Issuance of common stock for settlement of contingent consideration		6,279			6,279
Issuance of common stock for settlement of contingent consideration, Shares	232
Issuance of common stock under equity incentive plans	$ 1	1,554			1,555
Issuance of common stock under equity incentive plans, Shares	781
Issuance of common stock under employee stock purchase plan		2,383			2,383
Issuance of common stock under employee stock purchase plan, Shares	130
Share-based employee compensation expense		16,495			16,495
Other comprehensive income (loss)				(233)	(233)
Net loss			(21,137)		(21,137)
Ending Balance at Dec. 31, 2018	$ 39	$ 496,544	$ (247,003)	$ (199)	$ 249,381
Ending Balance, Shares at Dec. 31, 2018	38,604

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities:
Net loss	$ (21,137)	$ (26,892)	$ (33,338)
Adjustments to reconcile net loss to net cash used in operating activities:
Share-based compensation expense	16,495	14,615	11,697
Depreciation	7,244	7,761	7,655
Amortization of intangible assets	1,510	1,367	1,644
Amortization of deferred financing costs	515	264	218
Loss on disposal of property and equipment	323	336	433
Realized loss (gain) from foreign exchange on intercompany transactions	165	(173)	407
Amortization (accretion) of investments	(362)	30	126
Provision for doubtful accounts	598	(172)	149
Change in value of contingent consideration	(10,825)	(4,078)	969
Payment of contingent consideration in excess of purchase accounting amount	(96)
Changes in operating assets and liabilities:
Accounts receivable	(2,837)	(1,464)	(1,982)
Inventories	(146)	(4,477)	(79)
Other current assets	(367)	829	122
Accounts payable	(2,398)	1,290	(1,072)
Accrued liabilities	7,016	2,228	(1,915)
Other noncurrent assets and liabilities	131	(408)	(153)
Net cash used in operating activities	(4,171)	(8,944)	(15,119)
Cash flows from investing activities:
Purchases of available-for-sale securities	(106,588)	(16,455)	(28,592)
Sales and maturities of available-for-sale securities	27,389	26,600	24,202
Purchases of property and equipment	(6,211)	(6,384)	(7,692)
Proceeds from sale of property and equipment	6		3
Net cash (used in) provided by investing activities	(85,404)	3,761	(12,079)
Cash flows from financing activities:
Proceeds from sale of stock, net of offering costs of $229	82,873
Proceeds from debt borrowings	17,381		25,000
Payments on debt and capital leases	(1,755)	(1,689)	(439)
Payment of debt fees	(1,136)	(50)	(120)
Proceeds from stock option exercises	6,012	4,402	3,337
Shares repurchased for payment of taxes on stock awards	(4,457)	(2,013)	(1,701)
Proceeds from issuance of common stock under employee stock purchase plan	2,383	2,110	1,618
Payment of contingent consideration amounts established in purchase accounting	(1,125)
Net cash provided by financing activities	100,176	2,760	27,695
Effect of exchange rate changes on cash and cash equivalents	(179)	24	(53)
Net increase (decrease) in cash and cash equivalents	10,422	(2,399)	444
Cash and cash equivalents-beginning of period	21,809	24,208	23,764
Cash and cash equivalents-end of period	32,231	21,809	24,208
Supplemental cash flow information:
Cash paid for interest	3,870	2,002	1,506
Cash paid for income taxes	65	37	30
Non-cash investing and financing activities:
Accrued purchases of property and equipment	348	650	340
Assets acquired through capital lease	24	$ 2	152
Share-settled portion of contingent consideration	6,279
Capital lease asset early termination	$ 6		$ (37)

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)
Condensed Consolidated Statements of Cash Flows [Abstract]
Offering cost for sale of stock	$ 229

Description of Business and Sum

Description of Business and Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2018
Description of Business and Summary of Significant Accounting Policies [Abstract]
Description of Business and Summary of Significant Accounting Policies	1. DE SCRIPTION 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 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; AtriCure Hong Kong Limited, the Company’s wholly-owned subsidiary incorporated in Hong Kong; and AtriCure (Beijing) Medicine Information Consulting Services, Co., Ltd., AtriCure Hong Kong Limited’s wholly-owned subsidiary incorporated in Beijing. 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 . Investments— The Company places its investments primarily in U.S. Government agencies and securities, corporate bonds, commercial paper and asset-backed securities 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. Revenue Recognition— The Company recognizes revenue when control of promised goods is transferred to customers in an amount that reflects the consideration the Company expects to be entitled to in exchange for those goods. This generally occurs upon shipment of goods to customers. See Note 11 for further discussion on revenue. Sales Returns and Allowances — T he Company maintains a provision for potential returns of defective or damaged products, products shipped in error and invoice adjustments. 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 and the provision is included in accrued liabilities. 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 s . 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 regulatory approvals, variability in product launch strategies and variation in product use all impact inventory reserves for excess, obsolete and expired products. An 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 served by our direct sales force . 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. 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. The Company reassesses the useful lives of intangible assets annually . Included in intangible assets is In Process Research and Development (IPR&D) , representing 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 may 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 at least annually. The Company has historically tested IPR&D for impairment annually on November 30. In 2018, the Company has changed its testing date from November 30 to October 1. This change in the method of applying an accounting principle is preferred as it better aligns with the Company’s long-term planning process, which is a significant input to the testing, and it did not result in a material change to the Company's Consolidated Financial Statements. Goodwill— Goodwill represents the excess of purchase price over the fair value of the net assets acquired in business combinations. The Company’s goodwill is accounted for in a single reporting unit representing the Company as a whole. The Company has historically tested goodwill for impairment annually on November 30, or more often if impairment indicators are present. In 2018, the Company has changed its goodwill testing date from November 30 to October 1. This change in the method of applying an accounting principle is preferred by the Company as it better aligns with the Company’s long-term planning process, which is a significant input to the testing, and it did not result in a material change to the Company’s Consolidated Financial Statements. Other Noncurrent Liabilities— Other noncurrent liabilities consist of contingent consideration recorded in business combinations, deferred revenues and other contractual obligations. T he contingent consideration balance is included in noncurrent liabilities as such settlement is both required and expected to be made primarily 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 denominated 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. 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 3, 869 , 4,321 and 4,320 stock options , restricted stock awards, restricted stock units and performance share awards as of December 31, 2018, 2017 and 2016 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 o ther comprehensive (loss) income consisted of the following (net of tax):      2018 2017 2016  Total accumulated other comprehensive income (loss) at beginning of period $ 34 $ (468) $ (611)  Unrealized losses on investments  Balance at beginning of period $ (6) $ (21) $ (39)  Other comprehensive (loss) income before reclassifications (31) 15 18  Amounts reclassified from accumulated other comprehensive (loss) income to other income — — —  Balance at end of period $ (37) $ (6) $ (21)  Foreign currency translation adjustment  Balance at beginning of period $ 40 $ (447) $ (572)  Other comprehensive (loss) income before reclassifications (367) 660 532  Amounts reclassified from accumulated other comprehensive (loss) income to other income 165 (173) (407)  Balance at end of period $ (162) $ 40 $ (447)  Total accumulated other comprehensive (loss) income at end of period $ (199) $ 34 $ (468) 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 $785 , $900 and $625 during the years ended December 31, 2018, 2017 and 2016. 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, performance shares and stock purchases related to an employee stock purchase plan, based on estimated fair values. 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 awards, restricted stock units and performance share awards 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 investments in U.S. government agencies and securities, accounts receivable, short-term other assets, accounts payable and accrued liabilities 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, commercial paper and asset-backed securities 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 because the interest rate varies with market rates. Significant unobservable inputs with respect to the fair value measurement of the Level 3 contingent consideration liability are developed using Company data. See Note 3 – Fair Value for further information on fair value measurements.

Recent Accounting Pronouncement

Recent Accounting Pronouncements	12 Months Ended
	Dec. 31, 2018
Recent Accounting Pronouncements [Abstract]
Recent Accounting Pronouncements	2. RECENT ACCOUNTING PRONOUNCEMENTS In February 2016, the FASB issued ASU 2016-02, “Leases” (ASU 2016-02), codified as ASC 842, 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 interim and annual reporting periods beginning within 2019. We plan to adopt the standard using the transition method provided by ASU 2018-11, “Leases (Topic 842): Targeted Improvements”. Under this method, we will apply the new requirements to only those leases that exist as of January 1, 2019, rather than at the earliest comparative period presented in the financial statements. Prior periods will be presented under existing lease guidance. Upon transition, we plan to apply the package of practical expedients permitted under ASC 842 transition guidance. As a result, we are not required to reassess (1) whether expired or existing contracts contain leases under the new definition of a lease, including whether an existing or expired contract contains an embedded lease, (2) lease classification for expired or existing leases and (3) any initial direct costs of existing leases. The Company is finalizing procedures to validate the completeness of arrangements that meet the new definition of operating lease, in parallel with our assessment of policy elections, processes and internal controls. T he Company currently estimates the adoption of this guidance will result in the recognition of right-of-use assets and lease liabilities for operating leases of approximately $2,000 to $4,000 as of January 1, 2019 . In January 2017, the FASB issued ASU 2017-04, “Intangibles - Goodwill and Other (Topic 350): Simplifying the Accounting for Goodwill Impairment” (ASU 2017-04). The guidance removes the requirement to perform a hypothetical purchase price allocation to measure goodwill impairment. Under ASU 2017-04, a goodwill impairment will be the amount by which a reporting unit’s carrying value exceeds its fair value, not to exceed the carrying amount of goodwill. The guidance becomes effective for annual reporting periods beginning after December 15, 2019 and interim periods within those fiscal years, with early adoption permitted, and applied prospectively. The Company is evaluating the provisions of ASU 2017-04 to determine the impact on its consolidated financial statements and related disclosures. In August 2018, the FASB issued ASU 2018-13, “Fair Value Measurement (Topic 820), Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement” (ASU 2018-13). The amendments modify the disclosure requirements for fair value measurements and are effective for all entities for interim and annual reporting periods beginning within 2020. Early adoption of either the entire standard or only the provisions that eliminate or modify the requirements is permitted. The Company is evaluating the provisions of ASU 2018-13 to determine the impact on its fair value measurement disclosures. In August 2018, the FASB issued ASU 2018-15, “Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract” (ASU 2018-15). The amendments in this ASU align the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software (and hosting arrangements that include an internal-use software license). Entities should apply the guidance in ASC 350-40 on internal-use software when capitalizing implementation costs related to a hosting arrangement that is a service contract and expense the capitalized implementation costs related to a hosting arrangement that is a service contract over the hosting arrangement's term, presenting the expense in the same line item in the statement of income as that in which the fee associated with the hosting arrangement is presented. The amendments are effective for all entities for interim and annual reporting periods beginning within 2020. Early adoption is permitted, and entities have the option of applying either a retrospective or prospective transition method. The Company is evaluating the provisions of ASU 2018-15 to determine the impact on its consolidated financial statements and related disclosures. In August 2018, the SEC issued a final rule that amends certain of its disclosure requirements. The final rule was effective as of November 5, 2018. Among other amendments, the final rule extends to interim periods the annual disclosure requirement of changes in stockholders’ equity. Under the amendments, an analysis of changes in each caption of stockholders’ equity presented in the balance sheet must be provided in a note or a separate statement. The analysis should present a reconciliation of the beginning balance of each period for which a statement of comprehensive income is required to be filed. The Company anticipates its first presentation of changes in stockholders’ equity will be included in its Form 10-Q for the quarter ended March 31, 2019.

Fair Value

Fair Value	12 Months Ended
	Dec. 31, 2018
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, 2018:      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 $ — $ 16,193 $ — $ 16,193  Commercial paper — 40,731 — 40,731  U.S. government agencies and securities 6,734 — — 6,734  Corporate bonds — 30,195 — 30,195  Asset-backed securities — 14,511 — 14,511  Total assets $ 6,734 $ 101,630 $ — $ 108,364  Liabilities:  Acquisition-related contingent consideration $ — $ — $ 18,773 $ 18,773  Total liabilities $ — $ — $ 18,773 $ 18,773  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  There were no changes in the levels or methodology of measurement of financial assets and liabilities during the years ended December 31, 2018 and 2017.  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. The Company completed patient enrollment on August 21, 2018, and payment was made to former nContact shareholders on September 20, 2018. · 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. No payments were made for calendar years 2016 through 2018 as revenues did not exceed the targets for these years. 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. As a result of the achievement of the trial enrollment milestone, the Company made cash payments totaling approximately $1,221 and issued and delivered 232 shares of common stock to the former shareholders of nContact on September 20, 2018. 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 and timing of achievement of the agreed milestones, projected revenues 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. The contingent consideration liability is recorded in other noncurrent liabilities. Subsequent revisions to key assumptions, which impact the estimated fair value of contingent consideration liabilities, are recorded in selling, general and administrative expenses. The fair value of the nContact contingent consideration was remeasured during 2018, resulting in a decrease in fair value of $10,825 . This decrease in fair value is due to actual 2018 revenues falling below the commercial milestone target, a decrease in forecasted 2019 revenues for the 2019 commercial milestone, and changes in estimates related to the timing of achievement of the regulatory milestone as a result of the completion of enrollment in the CONVERGE IDE clinical trial in 2018. Adjustments to fair value are recorded in selling, general and administrative expenses. 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:      2018 2017 2016  Beginning Balance – January 1 $ 37,098 $ 41,176 $ 40,207  Settlement of trial enrollment milestone (7,500) — —  Changes in fair value included in selling, general and administrative expenses (10,825) (4,078) 969  Ending Balance – December 31 $ 18,773 $ 37,098 $ 41,176

Investments

Investments	12 Months Ended
	Dec. 31, 2018
Investments [Abstract]
Investments	4. INVESTMENTS Investments as of December 31, 2018 consisted of the following:      Unrealized  Gains  Cost Basis (Losses) Fair Value  Corporate bonds $ 30,223 $ (28) $ 30,195  U.S. government agencies and securities 6,734 — 6,734  Commercial paper 40,731 — 40,731  Asset-backed securities 14,520 (9) 14,511  Total $ 92,208 $ (37) $ 92,171  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  The Company has not experienced any significant realized gains or losses on its investments in the years ended December 31, 2018, 2017 and 2016.

Intangible Assets And Goodwill

Intangible Assets And Goodwill	12 Months Ended
	Dec. 31, 2018
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:      2018 2017  Estimated Accumulated Accumulated  Useful Life Cost Amortization Cost Amortization  Fusion technology 8 years $ 9,242 $ 4,763 $ 9,242 $ 3,697  Clamp & probe technology 3 years 829 829 829 829  SUBTLE access technology 5 years 2,179 1,425 2,179 981  IPR&D 44,021 — 44,021 —  Total $ 56,271 $ 7,017 $ 56,271 $ 5,507  Amortization expense related to intangible assets with definite lives, which excludes the IPR&D asset, was $1,510 , $1,367 and $1,644 for the years ended December 31, 2018, 2017 and 2016. In 2018, the Company reduced the ten-year estimated useful life of the Fusion technology asset by two years based on changes in estimated periods benefited. This change in estimate resulted in additional amortization expense of $143 in 2018 and will be applied prospectively. Intangible assets with definite lives will be fully amortized in 2021. Future amortization expense is projected as follows:      2019 $ 1,936  2020 1,804  2021 1,493  Total $ 5,233  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, 2016 $ 105,257  Additions (impairments) —  Net carrying amount as of December 31, 2017 105,257  Additions (impairments) —  Net carrying amount as of December 31, 2018 $ 105,257

Inventories

Inventories	12 Months Ended
	Dec. 31, 2018
Inventories [Abstract]
Inventories	6. INVENTORIES Inventories consisted of the following at December 31:      2018 2017  Raw materials $ 9,100 $ 7,755  Work in process 1,232 1,299  Finished goods 12,152 13,397  Inventories $ 22,484 $ 22,451

Property and Equipment

Property and Equipment	12 Months Ended
	Dec. 31, 2018
Property and Equipment [Abstract]
Property and Equipment	7. PROPERTY AND EQUIPMENT Property and equipment consisted of the following at December 31:      Estimated Useful Life 2018 2017  Generators and other capital equipment 1 -3 years $ 18,158 $ 15,754  Building under capital lease 15 years 14,250 14,250  Computer and other office equipment 3 years 6,360 5,873  Machinery, equipment and vehicles 3 -7 years 4,859 4,576  Furniture and fixtures 3 -7 years 4,702 4,366  Leasehold improvements 5 -15 years 3,943 3,636  Construction in progress N/A 1,868 1,810  Equipment under capital leases 3 -5 years 213 221  Total 54,353 50,486  Less accumulated depreciation (27,273) (21,737)  Property and equipment, net $ 27,080 $ 28,749  Property and equipment depreciation expense was $7,244 , $7,761 and $7,655 for the years ended December 31, 2018, 2017 and 2016. Depreciation related to generators and other capital equipment was $3,191 , $3,574 and $3,591 in 2018, 2017 and 2016. As of December 31, 2018 and 2017, the net carrying value of generators and other capital equipment was $4,545 and $4,656 .

Accrued Liabilities

Accrued Liabilities	12 Months Ended
	Dec. 31, 2018
Accrued Liabilities [Abstract]
Accrued Liabilities	8. ACCRUED LIABILITIES Accrued liabilities consisted of the following at December 31:      2018 2017  Accrued bonus $ 9,100 $ 4,726  Accrued commissions 8,065 6,964  Accrued payroll and employee-related expenses 4,512 4,097  Sales returns and allowances 1,410 1,169  Other accrued liabilities 1,205 695  Accrued taxes and value-added taxes payable 886 634  Accrued royalties 662 626  Total $ 25,840 $ 18,911

Indebtedness

Indebtedness	12 Months Ended
	Dec. 31, 2018
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 effective February 23, 2018 and as further amended on December 28, 2018, includes 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 term loan and revolving credit facility both mature or expire, as applicable, in February 2023 . Principal payments of the term loan are to be made ratably commencing September 2019 through the loan’s maturity date. If the Company meets certain conditions, as specified by the Loan 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 0.50% or 5.00% . Financing costs related to the term loan of $6 20 are netted against the outstanding loan balance in the Consolidated Balance Sheets and amortized ratably over the term of the Loan Agreement. The revolving line of credit is subject to an annual facility fee of 0 .33% of the revolving line of credit, and any borrowings thereunder bear interest at the greater of the Prime Rate or 4.50% . Borrowing availability under the revolving credit facility is based on the lesser of $20,000 or a borrowing base calculation as defined by the Loan Agreement. As of December 31, 2018, the Company had no borrowings under the revolving credit facility and had borrowing availability of $20,000 . Financing costs related to the revolving line of credit are included in other assets in the Consolidated Balance Sheets and amortized ratably over the twelve-month period of the annual fee. The Loan Agreement also provides for certain prepayment and early termination fees if repaid before January 2020, as well as establishes a minimum liquidity covenant and dividend restrictions, along with other customary terms and conditions. Specified assets have been pledged as collateral. Capital Lease Obligations . As of December 31, 2018, 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, 2018, the cost of the leased assets, both building and computer equipment, was $14,463 , and accumulated amortization on the capital lease assets was $3,198 . 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 is renewed annually and remains outstanding as of December 31, 2018. Future maturities on debt and capital lease obligations are projected as follows:      2019 $ 5,303  2020 12,942  2021 12,947  2022 12,968  2023 3,467  2024 and thereafter 11,393  Total payments $ 59,020  Imputed interest on capital lease obligations (6,225)  Net debt obligations, of which $4,433 is current and $48,362 is noncurrent $ 52,795

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2018
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:      2019 $ 1,064  2020 893  2021 648  2022 405  Total $ 3,010 Rent expense was $1,146 , $850 and $1,250 in 2018, 2017, and 2016. Royalty Agreements. The Company has certain royalty agreements in place with terms that include payment of royalties of 3% to 5% of specified product sales. The current royalty agreements have effective dates as early as 2003 and terms ranging from eighteen years to at least twenty years. Parties to the royalty agreements have the right at any time to terminate the agreement immediately for cause. Royalty expense of $2,715 , $2,323 and $1,895 was recorded as part of cost of revenue for the years ended December 31, 2018, 2017 and 2016. Purchase Agreements. The Company enters into standard purchase agreements with certain vendors in the ordinary course of business. Outstanding commitments at December 31, 2018 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. The Company received a Civil Investigative Demand (CID) from the U.S. Department of Justice (USDOJ) in December 2017 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 2010 to December 2017 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. The Company provided the USDOJ with documents and answers to the written interrogatories and is cooperating with its investigation. However, the Company cannot predict when the investigation will be resolved, the outcome of the investigation or its potential impact on the Company.

Revenue

Revenue	12 Months Ended
	Dec. 31, 2018
Revenue [Abstract]
Revenue	11. REVENUE The Company adopted FASB ASC 606, “Revenue from Contracts with Customers” (ASC 606) using the modified retrospective method effective January 1, 2018. The adoption of ASC 606 did not have a material impact on the amount and timing of revenue recognized in the Consolidated Financial Statements. Revenue is generated primarily from the sale of medical devices. The Company recognizes revenue in an amount that reflects the consideration the Company expects to be entitled to in exchange for those devices when control of promised devices is transferred to customers. At contract inception, the Company assesses the products promised in its contracts with customers and identifies a performance obligation for each promise to transfer to the customer a product that is distinct. The Company’s devices are distinct and represent performance obligations. These performance obligations are satisfied and revenue is recognized at a point in time upon shipment or delivery of products. Sales of devices are categorized as follows: open-heart ablation, minimally invasive ablation (MIS), appendage management and valve tools. Shipping and handling activities performed after control over products transfers to customers are considered activities to fulfill the promise to transfer the products rather than as separate promises to customers. Revenue includes shipping and handling revenue of $1,236 , $1,090 and $1,266 in 2018, 2017 and 2016. Products are sold primarily through a direct sales force and through distributors in certain 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. 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 in order to render products operational. Significant judgments and estimates involved in the Company’s recognition of revenue include the determination of the timing of transfer of control of products to customers and the estimation of a provision for returns. The Company considers the following indicators when determining when the control of products transfers to customers: (i) the Company has a right to payment in accordance with the shipping terms set forth in its contracts with customers; (ii) customers have legal title to products in accordance with shipping terms; (iii) the Company transfers physical possession of products either when the Company presents the products to a third party carrier for delivery to a customer (FOB shipping point) or when a customer receives the delivered goods (FOB destination); (iv) customers have the significant risks and rewards of ownership of products; and (v) customers have accepted products in connection with contractual shipping terms. In the normal course of business, the Company does not accept product returns unless a product is defective as manufactured. The Company establishes estimated provisions for returns based on historical experience. The Company does not provide customers with the right to a refund. The Company expects to be entitled to the total consideration for the products ordered by customers as product pricing is fixed according to the terms of customer contracts and payment terms are short. Payment terms fall within the one-year guidance for the practical expedient which allows the Company to forgo adjustment of the promised amount of consideration for the effects of a significant financing component. The Company excludes taxes assessed by governmental authorities on revenue-producing transactions from the measurement of the transaction price. Costs associated with product sales include commissions and royalties. Considering that product sales are performance obligations in contracts that are satisfied at a point in time, commission expense associated with product sales and royalties paid based on sales of certain products is incurred at that point in time rather than over time. Therefore, the Company applies the practical expedient and recognizes commissions and royalties as expense when incurred because the expense is incurred at a point in time and the amortization period is less than one year. Commissions are recorded as selling expense and royalties are recorded as cost of revenue. See Note 16 for disaggregated revenue by geographic area and by product category.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2018
Income Taxes [Abstract]
Income Tax Provision	12. 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. 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 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. On December 22, 2017, the SEC staff also issued Staff Accounting Bulletin No. 118 (SAB 118) which allowed businesses to record provisional amounts in the application of U.S. GAAP during a measurement period, not to extend beyond one year from the enactment of the Tax Reform Act, in situations when a registrant did 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 completed our accounting for the tax effects of enactment of the Tax Reform Act which resulted in the following: 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. Interest Limitation: The Tax Reform Act limits a Company’s interest deduction to 30% of tax earnings before interest, tax, depreciation and amortization beginning in 2018 through 2021. Thereafter, the interest deduction is limited to 30% of tax earnings before interest and taxes. Any disallowed interest in a year becomes a separate deferred tax asset with an indefinite carryforward period that can be utilized by a Company in a future tax year by an amount equal to its interest limitation in excess of its interest expense for that year. In 2018, the Company’s net interest expense of $3 ,131 was disallowed and became a $774 deferred tax asset on which a full valuation allowance was recorded. 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. In 2018, the Company completed its analysis of all of its relevant equity compensation agreements and recorded a reduction to its federal deferred tax assets of $2,482 with an offsetting reduction in its valuation allowance at December 31, 2018. Corporate Alternative Minimum Tax (AMT): The repeal of AMT provides companies with the ability to obtain refunds of historic AMT credits. In 2018, the Company has recorded a current federal tax refund of $51 of its historic 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 intends to claim 100 percent bonus depreciation for eligible property in 2018. International Tax : The Tax Reform Act provides for a one-time "deemed repatriation" of accumulated foreign earnings for the year ended December 31, 2017. In addition, beginning in 2018 the Tax Reform Act imposes a new tax on global intangible low taxed income of foreign subsidiaries and provides a new deduction for foreign derived intangible income of a domestic company. The Company did not incur a tax on the deemed repatriation or its current year foreign earnings as a result of its foreign deficits and previously taxed foreign earnings. The Company also did not receive a deduction for its foreign derived income due to its net operating losses. The Tax Reform Act provided companies with the ability to elect to reclassify the income tax effects of the Tax Cuts and Jobs Act on items within accumulated other comprehensive income (loss) to retained earnings. The Company will not make this election due to its full valuation allowance. The detail of deferred tax assets and liabilities at December 31 is as follows:      2018 2017  Deferred tax assets (liabilities):  Net operating loss carryforward $ 68,563 $ 64,776  Research and development and AMT credit carryforwards, net 6,206 5,339  Deferred interest 774 —  Equity compensation 4,750 6,955  Accruals and reserves 802 874  Inventories 726 588  Intangible assets (11,448) (11,297)  Property and equipment, net (608) (339)  Other, net 135 179  Subtotal 69,900 67,075  Less valuation allowance (69,849) (66,973)  Total $ 51 $ 102  The Company’s provision for income taxes for each of the years ended December 31 is as follows:      2018 2017 2016  Current Tax Expense  Federal $ (51) $ — $ —  State 28 44 32  Foreign 198 72 8  Total current tax expense 175 116 40  Deferred Tax Expense  Federal $ (3,048) $ 18,485 $ (7,333)  State 178 (1,337) 210  Foreign 45 (2,241) (1,177)  Change in valuation allowance 2,876 (15,009) 8,300  Total deferred tax expense 51 (102) —  Total tax expense $ 226 $ 14 $ 40  The Company has federal net operating loss carryforwards of $239,162 whi ch have expirations between 2021 and 2038 and $18,228 which ha s no expiration as a result of the Tax Reform Act. The Company has state and local net operating loss carryforwards of $15 4 , 370 with varying expirations from 2019 to 2039 . 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 $6,154 which have expirations between 2023 and 2039 . Additionally, the Company has foreign net operating loss carryforwards of approximately $37,694 which have expirations between 2019 and 2028 . 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. The Company’s 2018, 2017 and 2016 effective income tax rates differ from the federal statutory rate as follows:      2018 2017 2016  Federal tax at statutory rate 21.00 % $ (4,391) 34.00 % $ (9,139) 34.00 % $ (11,322)  Federal and Foreign tax rate change (6.84) 1,430 (109.68) 29,480 — —  Federal R&D credit 4.39 (918) (0.40) 107 2.89 (962)  Federal deferred adjustment (10.77) 2,253 — — — —  Federal NOL adjustment for ASU — — 10.48 (2,816) — —  Valuation allowance (13.75) 2,876 55.84 (15,009) (24.93) 8,300  State income taxes (0.99) 206 4.81 (1,292) (0.69) 231  Foreign NOL adjustment (1.22) 256 1.30 (348) (1.36) 452  Foreign tax rate differential (0.60) 125 (2.45) 658 (1.62) 539  Permanent differences and other 7.70 (1,611) 6.05 (1,627) (8.41) 2,802  Effective tax rate (1.08) % $ 226 (0.05) % $ 14 (0.12) % $ 40  The Company’s pre-tax book loss for domestic and international operations was $(13,44 3 ) and $(7,468) for 2018, ( $19,409 ) and ( $7,469 ) for 2017 and ( $27,271 ) and ( $6,027 ) for 2016. The Company had undistributed earnings of foreign subsidiaries of approximately $234 at December 31, 2018. 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. H owever, 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 2018, 2017 and 2016 is presented below:      2018 2017 2016  Balance at the beginning of the year $ 1,157 $ 3,175 $ 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 $ 1,157 $ 3,175  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 income tax expense and the related tax liability. There are no amounts included in the balance of unrecognized tax benefits at December 31, 2018, 2017 and 2016 that, if recognized, would affect the effective tax rate. Included in the balance of unrecognized tax benefits at December 31, 2018 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, 2018.

Concentrations

Concentrations	12 Months Ended
	Dec. 31, 2018
Concentrations [Abstract]
Concentrations	13. CONCENTRATIONS During 2018, 2017 and 2016, approximately 10.8% , 13.2% and 14.4% of the Company’s total net revenue was derived from its top ten customers. During 2018, 2017 and 2016 no individual customer accounted for more than 10% of the Company’s revenue. As of December 31, 2018 and 2017, 11.8% and 19.7% 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, 2018 and 2017. The Company maintains cash and cash equivalents balances at financial institutions which at times exceed FDIC limits. As of December 31, 2018, $31,955 of the cash and cash equivalents balance was in excess of the FDIC limits.

Employee Benefit Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2018
Employee Benefit Plans [Abstract]
Employee Benefit Plans	14. 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 2018, 2017 and 2016 the Company made matching contributions of 50% on the first 6% of employee contributions to the 401(k) Plan. The Company’s matching contributions expensed during 2018, 2017 and 2016 were $1,560 , $1,367 and $1,222 . 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 2018, 2017 or 2016. The Company also provides retirement benefits for employees of AtriCure Europe and other foreign subsidiaries. Total contributions to retirement plans for these employees were $243 , $205 and $101 in 2018, 2017 and 2016.

Equity Compensation Plans

Equity Compensation Plans	12 Months Ended
	Dec. 31, 2018
Equity Compensation Plans [Abstract]
Equity Compensation Plans	15. EQUITY COMPENSATION PLANS The Company has two share-based incentive plans: the 2014 Stock Incentive Plan (2014 Plan) and the 2018 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 restricted stock awards, restricted stock units, collectively “RSAs”, nonstatutory stock options, performance share awards (PSAs) or stock appreciation rights to Company employees, directors and consultants. The administrator (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, 2018, 11,099 shares of common stock had been reserved for issuance under the 2014 Plan and 1,319 shares were available for future grants. Effective March 1, 2018, the Compensation Committee of the Board approved the grant of performance share awards (2018 PSAs) to the Company’s named executive officers and certain other executive employees pursuant to the Company’s 2014 Plan. The form of award agreement for the 2018 PSAs (2018 PSA Grant Form) provides, among other things, that (i) each 2018 PSA that vests represents the right to receive one share of the Company’s common stock; (ii) the 2018 PSAs vest based on the Company achieving specified performance measurements over a performance period of three years, beginning January 1, 2018; (iii) the performance measurements include revenue CAGR as defined in the 2018 PSA Grant Form; (iv) threshold, target and maximum payout opportunities established for the 2018 PSAs will be used to calculate the number of shares that will be issuable when the award vests, which may range from 0% to 200% of the target amount; (v) any 2018 PSAs that are earned are scheduled to vest and be settled in shares of the Company’s common stock at the end of the performance period; and (vi) all or a portion of the 2018 PSAs may vest following a change of control or a termination of service by reason of death or disability (each as described in greater detail in the 2018 PSA Grant Form). With respect to the 2018 PSAs, the number of shares that vest and are issued to the recipient is based upon the Company’s performance as measured against the specified targets at the end of the three -year performance period as determined by the Compensation Committee of the Board. The Company estimated the fair value of the 2018 PSAs based on its closing stock price on the grant date and will adjust compensation expense over the performance period based on its estimate of performance target achievement. Stock options granted prior to 2018 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 prior to 2018 generally vest between one and four years from the date of grant. Beginning in 2018, stock options, restricted stock awards, and restricted stock units granted generally vest in one-third increments on the first, second and third anniversaries of the grant date. Activity under the plans during 2018 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, 2018 2,026 $ 13.30  Granted 52 26.05  Exercised (474) 12.70  Cancelled (22) 18.14  Outstanding at December 31, 2018 1,582 $ 13.83 5.02 $ 26,587  Vested and expected to vest 1,574 $ 13.78 5.00 $ 26,525  Exercisable at December 31, 2018 1,419 $ 12.99 4.63 $ 24,991      Weighted Weighted  RSA Average PSA Average  Shares Grant Date Shares Grant Date  Restricted Stock Awards and Performance Share Awards Outstanding Fair Value Outstanding Fair Value  Outstanding at January 1, 2018 1,845 $ 18.22 — $ —  Awarded 630 18.71 90 17.71  Released (638) 18.87 — —  Forfeited (91) 17.97 — —  Outstanding at December 31, 2018 1,746 $ 18.19 90 $ 17.71      Weighted  Weighted Average  Number of Average Remaining Aggregate  Shares Exercise Contractual Intrinsic  Performance Stock Options Outstanding Price Term Value  Outstanding at January 1, 2018 450 $ 13.48  Granted — —  Exercised — —  Cancelled — —  Outstanding at December 31, 2018 450 $ 13.48 4.45 $ 5,555  Exercisable at December 31, 2018 350 $ 13.48 4.45 $ 4,321  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 Awards 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   The total intrinsic value of options exercised during the years ended December 31, 2018, 2017 and 2016 was $5,343 , $5,121 and $3,550 . 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 2018, 2017 and 2016, $6,012 , $4,402 and $3,337 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 2018, 2017 and 2016 was $11,864 , $6,235 and $5,102 . The Company issues registered shares of common stock to satisfy stock option exercises and restricted stock grants. 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 2018, 2017 and 2016 of $0 , $43 and $269 . 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. As of December 31, 2018, there were 595 shares available for future issuance under the ESPP. 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 2018, 2017 and 2016. The expense was allocated as follows:      2018 2017 2016  Cost of revenue $ 1,545 $ 610 $ 420  Research and development expenses 1,987 2,052 1,825  Selling, general and administrative expenses 12,963 11,953 9,452  Total $ 16,495 $ 14,615 $ 11,697 Share-based compensation expense with respect to the ESPP was $697 , $664 and 556 for 2018, 2017 and 2016. The Company recognized expense related to time-based stock options, restricted stock awards, and restricted stock units for 2018, 2017, and 2016 of $15,032 , $13,908 and $10,872 . The Company recognized expense of $766 related to performance share awards in 2018. As of December 31, 2018 there was $20,198 of unrecognized compensation costs related to non-vested stock options and restricted stock arrangements ( $1,432 relating to stock options and $18,766 relating to restricted stock). This cost is expected to be recognized over a weighted-average period of 2.0 years for stock options and 1.5 years for restricted stock. As of December 31, 2018 there was $1,869 of unrecognized compensation costs related to non-vested performance share awards , and th is cost is expected to be recognized over a weighted-average period of 1.9 years. 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:      2018 2017 2016  Risk-free interest rate 2.31 - 3.01 % 1.75 - 2.12 % 1.06 - 2.02 %  Expected life of option (years) 5.14 to 5.71 5.21 to 5.76 5.27 to 7.10  Expected volatility of stock 41.00 - 42.00 % 43.00 - 48.00 % 46.00 - 51.00 %  Weighted-average volatility 41.51 % 44.50 % 48.87 %  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, restricted stock units and performance share 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, restricted stock awards and performance share awards granted for 2018, 2017 and 2016 was as follows:       2018 2017 2016  Stock options $ 10.97 $ 8.60 $ 8.25  Restricted stock awards 18.71 19.38 16.35  Performance share awards 17.71 — — 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 Informat

Segment and Geographic Information	12 Months Ended
	Dec. 31, 2018
Segment and Geographic Information [Abstract]
Segment and Geographic Information	16. 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:      2018 2017 2016  United States $ 162,146 $ 138,387 $ 122,385  Europe 25,912 21,901 19,772  Asia 12,687 13,616 12,223  Other international 885 812 729  Total international 39,484 36,329 32,724  Total revenue $ 201,630 $ 174,716 $ 155,109  United States revenue by product type was as follows:      2018 2017 2016  Open-heart ablation $ 72,250 $ 64,517 $ 58,050  Minimally invasive ablation 35,053 34,421 31,169  Appendage management 52,891 37,281 30,321  Total ablation and appendage management 160,194 136,219 119,540  Valve tools 1,952 2,168 2,845  Total United States $ 162,146 $ 138,387 $ 122,385  International revenue by product type was as follows:      2018 2017 2016  Open-heart ablation $ 21,118 $ 20,718 $ 20,189  Minimally invasive ablation 9,176 8,007 8,065  Appendage management 8,988 7,251 3,986  Total ablation and appendage management 39,282 35,976 32,240  Valve tools 202 353 484  Total international $ 39,484 $ 36,329 $ 32,724  The Company’s long-lived assets are located primarily in the United States, except for $1,296 as of December 31, 2018 and $957 as of December 31, 2017, which are located primarily in Europe.

Selected Quarterly Financial Da

Selected Quarterly Financial Data	12 Months Ended
	Dec. 31, 2018
Selected Quarterly Financial Data [Abstract]
Selected Quarterly Financial Data	17. SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED)     For the Three Months Ended  March 31, June 30, September 30, December 31,  2018 2017 2018 2017 2018 2017 2018 2017  Operating Results:  Revenue $ 46,994 $ 41,273 $ 51,802 $ 45,231 $ 49,941 $ 42,150 $ 52,893 $ 46,062  Gross profit 34,503 30,008 38,079 32,554 35,948 30,918 38,590 32,683  Income (loss) from operations (9,430) (9,642) 958 (6,355) (6,048) (6,847) (2,607) (2,135)  Net loss (10,134) (10,183) (338) (6,883) (7,235) (7,246) (3,430) (2,580)  Net loss per share (basic and diluted) $ (0.31) $ (0.32) $ (0.01) $ (0.21) $ (0.22) $ (0.22) $ (0.09) $ (0.08)  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 Qua

Schedule II - Valuation And Qualifying Accounts	12 Months Ended
	Dec. 31, 2018
SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]
Schedule of Valuation and Qualifying Accounts Disclosure	SCH EDULE II VALUATION AND QUALIFYING ACCOUNTS     Beginning Ending  Balance Additions Deductions Balance  Reserve for sales returns and allowances  Year ended December 31, 2018 $ 1,169 $ 312 $ 71 $ 1,410  Year ended December 31, 2017 834 441 106 1,169  Year ended December 31, 2016 207 634 7 834  Allowance for inventory valuation  Year ended December 31, 2018 $ 889 $ 718 $ 578 $ 1,029  Year ended December 31, 2017 1,080 1,004 1,195 889  Year ended December 31, 2016 843 1,692 1,455 1,080  Valuation allowance for deferred tax assets  Year ended December 31, 2018 $ 66,973 $ 2,876 $ — $ 69,849  Year ended December 31, 2017 81,982 — 15,009 66,973  Year ended December 31, 2016 73,682 8,300 — 81,982

Description of Business and S_2

Description of Business and Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2018
Description of Business and Summary of Significant Accounting Policies [Abstract]
Nature of the Business	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 sells its products to medical centers globally through its direct sales force and distributors.
Principles of Consolidation	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; AtriCure Hong Kong Limited, the Company’s wholly-owned subsidiary incorporated in Hong Kong; and AtriCure (Beijing) Medicine Information Consulting Services, Co., Ltd., AtriCure Hong Kong Limited’s wholly-owned subsidiary incorporated in Beijing. All intercompany accounts and transactions have been eliminated in consolidation.
Cash And Cash Equivalents	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
Investments	Investments— The Company places its investments primarily in U.S. Government agencies and securities, corporate bonds, commercial paper and asset-backed securities 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.
Revenue Recognition	Revenue Recognition— The Company recognizes revenue when control of promised goods is transferred to customers in an amount that reflects the consideration the Company expects to be entitled to in exchange for those goods. This generally occurs upon shipment of goods to customers. See Note 11 for further discussion on revenue.
Sales Returns and Allowances	Sales Returns and Allowances — T he Company maintains a provision for potential returns of defective or damaged products, products shipped in error and invoice adjustments. 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 and the provision is included in accrued liabilities.
Allowance for Doubtful Accounts Receivable	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 s . 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— 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 regulatory approvals, variability in product launch strategies and variation in product use all impact inventory reserves for excess, obsolete and expired products. An 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— 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 served by our direct sales force . 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. 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— Intangible assets with determinable useful lives are amortized on a straight-line basis over the estimated periods benefited. The Company reassesses the useful lives of intangible assets annually . Included in intangible assets is In Process Research and Development (IPR&D) , representing 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 may 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 at least annually. The Company has historically tested IPR&D for impairment annually on November 30. In 2018, the Company has changed its testing date from November 30 to October 1. This change in the method of applying an accounting principle is preferred as it better aligns with the Company’s long-term planning process, which is a significant input to the testing, and it did not result in a material change to the Company's Consolidated Financial Statements.
Goodwill	Goodwill— Goodwill represents the excess of purchase price over the fair value of the net assets acquired in business combinations. The Company’s goodwill is accounted for in a single reporting unit representing the Company as a whole. The Company has historically tested goodwill for impairment annually on November 30, or more often if impairment indicators are present. In 2018, the Company has changed its goodwill testing date from November 30 to October 1. This change in the method of applying an accounting principle is preferred by the Company as it better aligns with the Company’s long-term planning process, which is a significant input to the testing, and it did not result in a material change to the Company’s Consolidated Financial Statements.
Other Noncurrent Liabilities	Other Noncurrent Liabilities— Other noncurrent liabilities consist of contingent consideration recorded in business combinations, deferred revenues and other contractual obligations. T he contingent consideration balance is included in noncurrent liabilities as such settlement is both required and expected to be made primarily in shares of the Company’s common stock pursuant to the nContact merger agreement.
Other Income (Expense)	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 denominated in British Pounds.
Taxes	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.
Net Loss Per Share	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 3, 869 , 4,321 and 4,320 stock options , restricted stock awards, restricted stock units and performance share awards as of December 31, 2018, 2017 and 2016 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)	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 o ther comprehensive (loss) income consisted of the following (net of tax):      2018 2017 2016  Total accumulated other comprehensive income (loss) at beginning of period $ 34 $ (468) $ (611)  Unrealized losses on investments  Balance at beginning of period $ (6) $ (21) $ (39)  Other comprehensive (loss) income before reclassifications (31) 15 18  Amounts reclassified from accumulated other comprehensive (loss) income to other income — — —  Balance at end of period $ (37) $ (6) $ (21)  Foreign currency translation adjustment  Balance at beginning of period $ 40 $ (447) $ (572)  Other comprehensive (loss) income before reclassifications (367) 660 532  Amounts reclassified from accumulated other comprehensive (loss) income to other income 165 (173) (407)  Balance at end of period $ (162) $ 40 $ (447)  Total accumulated other comprehensive (loss) income at end of period $ (199) $ 34 $ (468) 
Research and Development Costs	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	Advertising Costs — The Company expenses advertising costs as incurred. Advertising expense was $785 , $900 and $625 during the years ended December 31, 2018, 2017 and 2016.
Share-Based Compensation	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, performance shares and stock purchases related to an employee stock purchase plan, based on estimated fair values. 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 awards, restricted stock units and performance share awards 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	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	Fair Value Disclosures — The Company classifies cash investments in U.S. government agencies and securities, accounts receivable, short-term other assets, accounts payable and accrued liabilities 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, commercial paper and asset-backed securities 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 because the interest rate varies with market rates. Significant unobservable inputs with respect to the fair value measurement of the Level 3 contingent consideration liability are developed using Company data. See Note 3 – Fair Value for further information on fair value measurements.

Description of Business and S_3

Description of Business and Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2018
Description of Business and Summary of Significant Accounting Policies [Abstract]
Accumulated Other Comprehensive Income (Loss)	   2018 2017 2016  Total accumulated other comprehensive income (loss) at beginning of period $ 34 $ (468) $ (611)  Unrealized losses on investments  Balance at beginning of period $ (6) $ (21) $ (39)  Other comprehensive (loss) income before reclassifications (31) 15 18  Amounts reclassified from accumulated other comprehensive (loss) income to other income — — —  Balance at end of period $ (37) $ (6) $ (21)  Foreign currency translation adjustment  Balance at beginning of period $ 40 $ (447) $ (572)  Other comprehensive (loss) income before reclassifications (367) 660 532  Amounts reclassified from accumulated other comprehensive (loss) income to other income 165 (173) (407)  Balance at end of period $ (162) $ 40 $ (447)  Total accumulated other comprehensive (loss) income at end of period $ (199) $ 34 $ (468) 

Fair Value (Tables)

Fair Value (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2018:      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 $ — $ 16,193 $ — $ 16,193  Commercial paper — 40,731 — 40,731  U.S. government agencies and securities 6,734 — — 6,734  Corporate bonds — 30,195 — 30,195  Asset-backed securities — 14,511 — 14,511  Total assets $ 6,734 $ 101,630 $ — $ 108,364  Liabilities:  Acquisition-related contingent consideration $ — $ — $ 18,773 $ 18,773  Total liabilities $ — $ — $ 18,773 $ 18,773  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 
Level 3 Fair Value Measurements Using Significant Other Unobservable Inputs for Acquisition-Related Contingent Consideration	   2018 2017 2016  Beginning Balance – January 1 $ 37,098 $ 41,176 $ 40,207  Settlement of trial enrollment milestone (7,500) — —  Changes in fair value included in selling, general and administrative expenses (10,825) (4,078) 969  Ending Balance – December 31 $ 18,773 $ 37,098 $ 41,176 

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2018
Investments [Abstract]
Summary of Short-term Investments	Investments as of December 31, 2018 consisted of the following:      Unrealized  Gains  Cost Basis (Losses) Fair Value  Corporate bonds $ 30,223 $ (28) $ 30,195  U.S. government agencies and securities 6,734 — 6,734  Commercial paper 40,731 — 40,731  Asset-backed securities 14,520 (9) 14,511  Total $ 92,208 $ (37) $ 92,171  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 

Intangible Assets And Goodwill

Intangible Assets And Goodwill (Tables)	12 Months Ended
	Dec. 31, 2018
Intangible Assets And Goodwill [Abstract]
Company's Intangible Assets	   2018 2017  Estimated Accumulated Accumulated  Useful Life Cost Amortization Cost Amortization  Fusion technology 8 years $ 9,242 $ 4,763 $ 9,242 $ 3,697  Clamp & probe technology 3 years 829 829 829 829  SUBTLE access technology 5 years 2,179 1,425 2,179 981  IPR&D 44,021 — 44,021 —  Total $ 56,271 $ 7,017 $ 56,271 $ 5,507 
Future Amortization Expense Related to Intangible Assets with Definite Lives	   2019 $ 1,936  2020 1,804  2021 1,493  Total $ 5,233 
Summary of Company's Goodwill	   Net carrying amount as of December 31, 2016 $ 105,257  Additions (impairments) —  Net carrying amount as of December 31, 2017 105,257  Additions (impairments) —  Net carrying amount as of December 31, 2018 $ 105,257 

Inventories (Tables)

Inventories (Tables)	12 Months Ended
	Dec. 31, 2018
Inventories [Abstract]
Summary Of Inventories	   2018 2017  Raw materials $ 9,100 $ 7,755  Work in process 1,232 1,299  Finished goods 12,152 13,397  Inventories $ 22,484 $ 22,451 

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
	Dec. 31, 2018
Property and Equipment [Abstract]
Summary of Property and Equipment	   Estimated Useful Life 2018 2017  Generators and other capital equipment 1 -3 years $ 18,158 $ 15,754  Building under capital lease 15 years 14,250 14,250  Computer and other office equipment 3 years 6,360 5,873  Machinery, equipment and vehicles 3 -7 years 4,859 4,576  Furniture and fixtures 3 -7 years 4,702 4,366  Leasehold improvements 5 -15 years 3,943 3,636  Construction in progress N/A 1,868 1,810  Equipment under capital leases 3 -5 years 213 221  Total 54,353 50,486  Less accumulated depreciation (27,273) (21,737)  Property and equipment, net $ 27,080 $ 28,749 

Accrued Liabilities (Tables)

Accrued Liabilities (Tables)	12 Months Ended
	Dec. 31, 2018
Accrued Liabilities [Abstract]
Accrued Liabilities	   2018 2017  Accrued bonus $ 9,100 $ 4,726  Accrued commissions 8,065 6,964  Accrued payroll and employee-related expenses 4,512 4,097  Sales returns and allowances 1,410 1,169  Other accrued liabilities 1,205 695  Accrued taxes and value-added taxes payable 886 634  Accrued royalties 662 626  Total $ 25,840 $ 18,911 

Indebtedness (Tables)

Indebtedness (Tables)	12 Months Ended
	Dec. 31, 2018
Indebtedness [Abstract]
Future Maturities On Debt And Capital Lease Obligations	   2019 $ 5,303  2020 12,942  2021 12,947  2022 12,968  2023 3,467  2024 and thereafter 11,393  Total payments $ 59,020  Imputed interest on capital lease obligations (6,225)  Net debt obligations, of which $4,433 is current and $48,362 is noncurrent $ 52,795 

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies [Abstract]
Future Minimum Lease Payments Under Non-cancelable Operating Leases	   2019 $ 1,064  2020 893  2021 648  2022 405  Total $ 3,010 

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2018
Income Taxes [Abstract]
Summary of Detail of Deferred Tax Assets and Liabilities	   2018 2017  Deferred tax assets (liabilities):  Net operating loss carryforward $ 68,563 $ 64,776  Research and development and AMT credit carryforwards, net 6,206 5,339  Deferred interest 774 —  Equity compensation 4,750 6,955  Accruals and reserves 802 874  Inventories 726 588  Intangible assets (11,448) (11,297)  Property and equipment, net (608) (339)  Other, net 135 179  Subtotal 69,900 67,075  Less valuation allowance (69,849) (66,973)  Total $ 51 $ 102 
Summary Of Company's Provision for Income Taxes	   2018 2017 2016  Current Tax Expense  Federal $ (51) $ — $ —  State 28 44 32  Foreign 198 72 8  Total current tax expense 175 116 40  Deferred Tax Expense  Federal $ (3,048) $ 18,485 $ (7,333)  State 178 (1,337) 210  Foreign 45 (2,241) (1,177)  Change in valuation allowance 2,876 (15,009) 8,300  Total deferred tax expense 51 (102) —  Total tax expense $ 226 $ 14 $ 40 
Summary Of Difference Between Effective Income Tax Rates and Federal Statutory Rate	   2018 2017 2016  Federal tax at statutory rate 21.00 % $ (4,391) 34.00 % $ (9,139) 34.00 % $ (11,322)  Federal and Foreign tax rate change (6.84) 1,430 (109.68) 29,480 — —  Federal R&D credit 4.39 (918) (0.40) 107 2.89 (962)  Federal deferred adjustment (10.77) 2,253 — — — —  Federal NOL adjustment for ASU — — 10.48 (2,816) — —  Valuation allowance (13.75) 2,876 55.84 (15,009) (24.93) 8,300  State income taxes (0.99) 206 4.81 (1,292) (0.69) 231  Foreign NOL adjustment (1.22) 256 1.30 (348) (1.36) 452  Foreign tax rate differential (0.60) 125 (2.45) 658 (1.62) 539  Permanent differences and other 7.70 (1,611) 6.05 (1,627) (8.41) 2,802  Effective tax rate (1.08) % $ 226 (0.05) % $ 14 (0.12) % $ 40 
Summary Of Reconciliation of Change in Federal and State Unrecognized Tax Benefits	   2018 2017 2016  Balance at the beginning of the year $ 1,157 $ 3,175 $ 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 $ 1,157 $ 3,175 

Equity Compensation Plans (Tabl

Equity Compensation Plans (Tables)	12 Months Ended
	Dec. 31, 2018
Equity Compensation Plans [Abstract]
Activity Under Stock Based Compensation Plans	Activity under the plans during 2018 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, 2018 2,026 $ 13.30  Granted 52 26.05  Exercised (474) 12.70  Cancelled (22) 18.14  Outstanding at December 31, 2018 1,582 $ 13.83 5.02 $ 26,587  Vested and expected to vest 1,574 $ 13.78 5.00 $ 26,525  Exercisable at December 31, 2018 1,419 $ 12.99 4.63 $ 24,991      Weighted Weighted  RSA Average PSA Average  Shares Grant Date Shares Grant Date  Restricted Stock Awards and Performance Share Awards Outstanding Fair Value Outstanding Fair Value  Outstanding at January 1, 2018 1,845 $ 18.22 — $ —  Awarded 630 18.71 90 17.71  Released (638) 18.87 — —  Forfeited (91) 17.97 — —  Outstanding at December 31, 2018 1,746 $ 18.19 90 $ 17.71      Weighted  Weighted Average  Number of Average Remaining Aggregate  Shares Exercise Contractual Intrinsic  Performance Stock Options Outstanding Price Term Value  Outstanding at January 1, 2018 450 $ 13.48  Granted — —  Exercised — —  Cancelled — —  Outstanding at December 31, 2018 450 $ 13.48 4.45 $ 5,555  Exercisable at December 31, 2018 350 $ 13.48 4.45 $ 4,321  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 Awards 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  
Share-Based Compensation Expense Related to Employee Share-Based Compensation	   2018 2017 2016  Cost of revenue $ 1,545 $ 610 $ 420  Research and development expenses 1,987 2,052 1,825  Selling, general and administrative expenses 12,963 11,953 9,452  Total $ 16,495 $ 14,615 $ 11,697 
Assumptions Used for Determining Fair Value of Options	   2018 2017 2016  Risk-free interest rate 2.31 - 3.01 % 1.75 - 2.12 % 1.06 - 2.02 %  Expected life of option (years) 5.14 to 5.71 5.21 to 5.76 5.27 to 7.10  Expected volatility of stock 41.00 - 42.00 % 43.00 - 48.00 % 46.00 - 51.00 %  Weighted-average volatility 41.51 % 44.50 % 48.87 %  Dividend yield 0.00 % 0.00 % 0.00 % 
Weighted Average Estimated Grant Date Fair Value Per Share of Stock Options, Restricted Stock Granted, And Performance Awards	   2018 2017 2016  Stock options $ 10.97 $ 8.60 $ 8.25  Restricted stock awards 18.71 19.38 16.35  Performance share awards 17.71 — — 
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 Inform_2

Segment and Geographic Information (Tables)	12 Months Ended
	Dec. 31, 2018
Segment and Geographic Information [Abstract]
Revenue by Geographic Area	   2018 2017 2016  United States $ 162,146 $ 138,387 $ 122,385  Europe 25,912 21,901 19,772  Asia 12,687 13,616 12,223  Other international 885 812 729  Total international 39,484 36,329 32,724  Total revenue $ 201,630 $ 174,716 $ 155,109 
Revenue by Product Type	United States revenue by product type was as follows:      2018 2017 2016  Open-heart ablation $ 72,250 $ 64,517 $ 58,050  Minimally invasive ablation 35,053 34,421 31,169  Appendage management 52,891 37,281 30,321  Total ablation and appendage management 160,194 136,219 119,540  Valve tools 1,952 2,168 2,845  Total United States $ 162,146 $ 138,387 $ 122,385  International revenue by product type was as follows:      2018 2017 2016  Open-heart ablation $ 21,118 $ 20,718 $ 20,189  Minimally invasive ablation 9,176 8,007 8,065  Appendage management 8,988 7,251 3,986  Total ablation and appendage management 39,282 35,976 32,240  Valve tools 202 353 484  Total international $ 39,484 $ 36,329 $ 32,724 

Selected Quarterly Financial _2

Selected Quarterly Financial Data (Tables)	12 Months Ended
	Dec. 31, 2018
Selected Quarterly Financial Data [Abstract]
Schedule of Quarterly Financial Information	   For the Three Months Ended  March 31, June 30, September 30, December 31,  2018 2017 2018 2017 2018 2017 2018 2017  Operating Results:  Revenue $ 46,994 $ 41,273 $ 51,802 $ 45,231 $ 49,941 $ 42,150 $ 52,893 $ 46,062  Gross profit 34,503 30,008 38,079 32,554 35,948 30,918 38,590 32,683  Income (loss) from operations (9,430) (9,642) 958 (6,355) (6,048) (6,847) (2,607) (2,135)  Net loss (10,134) (10,183) (338) (6,883) (7,235) (7,246) (3,430) (2,580)  Net loss per share (basic and diluted) $ (0.31) $ (0.32) $ (0.01) $ (0.21) $ (0.22) $ (0.22) $ (0.09) $ (0.08) 

Description of Business and S_4

Description of Business and Summary of Significant Accounting Policies (Narrative) (Details) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Description Of Business And Significant Accounting Policies [Line Items]
Depreciation									$ 7,244	$ 7,761	$ 7,655
Net carrying amount of loaned equipment	$ 27,080				$ 28,749				27,080	28,749
Revenue	$ 52,893	$ 49,941	$ 51,802	$ 46,994	$ 46,062	$ 42,150	$ 45,231	$ 41,273	$ 201,630	$ 174,716	$ 155,109
Options, restricted stock and performance based shares excluded from calculation of net loss per share									3,869	4,321	4,320
Advertising costs									$ 785	$ 900	$ 625
Share-based compensation expense recognized									$ 16,495	$ 14,615	$ 11,697
Maximum [Member]
Description Of Business And Significant Accounting Policies [Line Items]
Maturity period of short term investment									1 year

Description of Business and S_5

Description of Business and Summary of Significant Accounting Policies (Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total accumulated other comprehensive income (loss) at beginning of period	$ 34	$ (468)	$ (611)
Total accumulated other comprehensive income (loss) at end of period	(199)	34	(468)
Unrealized Losses On Investments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total accumulated other comprehensive income (loss) at beginning of period	(6)	(21)	(39)
Other comprehensive income (loss)	(31)	15	18
Reclassification of accumulated other comprehensive income (loss) to other income (expense)
Total accumulated other comprehensive income (loss) at end of period	(37)	(6)	(21)
Foreign Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total accumulated other comprehensive income (loss) at beginning of period	40	(447)	(572)
Other comprehensive income (loss)	(367)	660	532
Reclassification of accumulated other comprehensive income (loss) to other income (expense)	165	(173)	(407)
Total accumulated other comprehensive income (loss) at end of period	$ (162)	$ 40	$ (447)

Fair Value (Narrative) (Details

Fair Value (Narrative) (Details) shares in Thousands	Sep. 20, 2018USD ($)shares	Oct. 13, 2015shares	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Change in value of contingent consideration			$ (10,825,000)	$ (4,078,000)	$ 969,000
Payments of contingent consideration			0	0	0
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			10,825,000
Fair value of AtriCure common stock issued at closing			5,660,000
Shares issued and delivered | shares	232	3,757
Payments of contingent consideration	$ 1,221,000
Significant Other Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Settlement of trial enrollment milestone one			(7,500,000)
Changes in fair value included in earnings			10,825,000	$ 4,078,000	$ (969,000)
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			$ 7,500,000
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			$ 42,500,000

Fair Value (Financial Assets an

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, 2018	Dec. 31, 2017
Assets:
Total assets	$ 108,364	$ 26,165
Liabilities:
Acquisition-related contingent consideration	18,773	37,098
Total liabilities	18,773	37,098
Money Market Funds [Member]
Assets:
Total assets	16,193	12,774
Commercial Paper [Member]
Assets:
Total assets	40,731	7,472
U.S. Government Securities [Member]
Assets:
Total assets	6,734	2,999
Corporate Bonds [Member]
Assets:
Total assets	30,195	2,920
Asset-backed Securities [Member]
Assets:
Total assets	14,511
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets:
Total assets	6,734	2,999
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | U.S. Government Securities [Member]
Assets:
Total assets	6,734	2,999
Significant Other Observable Inputs (Level 2) [Member]
Assets:
Total assets	101,630	23,166
Significant Other Observable Inputs (Level 2) [Member] | Money Market Funds [Member]
Assets:
Total assets	16,193	12,774
Significant Other Observable Inputs (Level 2) [Member] | Commercial Paper [Member]
Assets:
Total assets	40,731	7,472
Significant Other Observable Inputs (Level 2) [Member] | Corporate Bonds [Member]
Assets:
Total assets	30,195	2,920
Significant Other Observable Inputs (Level 2) [Member] | Asset-backed Securities [Member]
Assets:
Total assets	14,511
Significant Other Unobservable Inputs (Level 3) [Member]
Liabilities:
Acquisition-related contingent consideration	18,773	37,098
Total liabilities	$ 18,773	$ 37,098

Fair Value (Level 3 Fair Value

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, 2018	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 37,098	$ 41,176	$ 40,207
Settlement of trial enrollment milestone one	(7,500)
Changes in fair value included in selling, general and administrative expenses	(10,825)	(4,078)	969
Ending Balance	$ 18,773	$ 37,098	$ 41,176

Investments (Summary Of Short-t

Investments (Summary Of Short-term Investments) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Investment [Line Items]
Short-term investments, Cost Basis	$ 92,208	$ 12,648
Short-term investment, Unrealized gains (losses)	(37)	(6)
Short-term investments, Fair value	92,171	12,642
Corporate Bonds [Member]
Investment [Line Items]
Short-term investments, Cost Basis	30,223	2,925
Short-term investment, Unrealized gains (losses)	(28)	(5)
Short-term investments, Fair value	30,195	2,920
U.S. Government Securities [Member]
Investment [Line Items]
Short-term investments, Cost Basis	6,734	3,000
Short-term investment, Unrealized gains (losses)		(1)
Short-term investments, Fair value	6,734	2,999
Commercial Paper [Member]
Investment [Line Items]
Short-term investments, Cost Basis	40,731	6,723
Short-term investments, Fair value	40,731	$ 6,723
Asset-backed Securities [Member]
Investment [Line Items]
Short-term investments, Cost Basis	14,520
Short-term investment, Unrealized gains (losses)	(9)
Short-term investments, Fair value	$ 14,511

Intangible Assets And Goodwil_2

Intangible Assets And Goodwill (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Intangible Assets And Goodwill [Abstract]
Amortization of intangible assets	$ 1,510	$ 1,367	$ 1,644
Additional amortization expense	$ 143

Intangible Assets (Company's In

Intangible Assets (Company's Intangible Assets) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Cost	$ 56,271	$ 56,271
Accumulated Amortization	$ 7,017	5,507
Fusion Technology [Member]
Finite-Lived Intangible Assets [Line Items]
Estimated Useful Life	8 years
Cost	$ 9,242	9,242
Accumulated Amortization	$ 4,763	3,697
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	1,425	981
IPR&D [Member]
Finite-Lived Intangible Assets [Line Items]
Cost	$ 44,021	$ 44,021

Intangible Assets (Future Amort

Intangible Assets (Future Amortization Expense Related to Intangible Assets with Definite Lives) (Details) $ in Thousands	Dec. 31, 2018USD ($)
Intangible Assets And Goodwill [Abstract]
2,019	$ 1,936
2,020	1,804
2,021	1,493
Total	$ 5,233

Intangible Assets and Goodwil_3

Intangible Assets and Goodwill (Summary Of Company's Goodwill) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Intangible Assets And Goodwill [Abstract]
Goodwill, Beginning Balance	$ 105,257	$ 105,257
Additions (impairments)
Goodwill, Ending Balance	$ 105,257	$ 105,257

Inventories (Summary Of Invento

Inventories (Summary Of Inventories) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Inventories [Abstract]
Raw materials	$ 9,100	$ 7,755
Work in process	1,232	1,299
Finished goods	12,152	13,397
Inventories	$ 22,484	$ 22,451

Property and Equipment (Narrati

Property and Equipment (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Depreciation	$ 7,244	$ 7,761	$ 7,655
Net carrying amount of loaned equipment	27,080	28,749
Generators and Related Equipment [Member]
Property, Plant and Equipment [Line Items]
Depreciation	3,191	3,574	$ 3,591
Net carrying amount of loaned equipment	$ 4,545	$ 4,656

Property and Equipment (Summary

Property and Equipment (Summary Of Property And Equipment) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 54,353	$ 50,486
Less accumulated depreciation	(27,273)	(21,737)
Property, and equipment, net	27,080	28,749
Generators and Related Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	18,158	15,754
Property, and equipment, net	$ 4,545	4,656
Building under Capital Lease [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	15 years
Property and equipment, gross	$ 14,250	14,250
Computers, Software and Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	3 years
Property and equipment, gross	$ 6,360	5,873
Machinery And Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	4,859	4,576
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	4,702	4,366
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	3,943	3,636
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	1,868	1,810
Equipment under Capital Leases [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 213	$ 221
Minimum [Member] | Generators and Related Equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	1 year
Minimum [Member] | Machinery And Equipment [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 Related Equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	minus 3 years
Maximum [Member] | Machinery And Equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	minus 7 years
Maximum [Member] | Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	minus 7 years
Maximum [Member] | Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	minus 15 years
Maximum [Member] | Equipment under Capital Leases [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	minus 5 years

Accrued Liabilities (Accrued Li

Accrued Liabilities (Accrued Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accrued Liabilities [Abstract]
Accrued bonus	$ 9,100	$ 4,726
Accrued commissions	8,065	6,964
Accrued payroll and employee-related expenses	4,512	4,097
Sales returns and allowances	1,410	1,169
Other accrued liabilities	1,205	695
Accrued royalties	662	626
Accrued taxes	886	634
Total	$ 25,840	$ 18,911

Indebtedness (Narrative) (Detai

Indebtedness (Narrative) (Details) - USD ($)	Feb. 23, 2018	Dec. 31, 2018
Line of Credit Facility [Line Items]
Cost of assets under lease		$ 14,463,000
Accumulated amortization on the capital leases		$ 3,198,000
Maximum [Member]
Line of Credit Facility [Line Items]
Loan term		1 year
Silicon Valley Bank, Amended And Restated Loan Agreement Effective 2/23/18 [Member]
Line of Credit Facility [Line Items]
Upon certain conditions met, deferred loan payment period	6 months
Silicon Valley Bank, Amended And Restated Loan Agreement Effective 2/23/18 [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of credit		$ 20,000,000
Maturity date		Feb. 28, 2023
Line of credit, amount outstanding		$ 0
Line of credit, availability		$ 20,000,000
Annual commitment fee, percentage		0.33%
Silicon Valley Bank, Amended And Restated Loan Agreement Effective 2/23/18 [Member] | Revolving Credit Facility [Member] | Prime Rate [Member]
Line of Credit Facility [Line Items]
Basis rate		4.50%
Computer And Office Equipment [Member]
Line of Credit Facility [Line Items]
Capital lease expiration period		Dec. 31, 2030
Term Loan [Member] | Silicon Valley Bank, Amended And Restated Loan Agreement Effective 2/23/18 [Member]
Line of Credit Facility [Line Items]
Loan amount	$ 40,000,000
Financing costs		$ 620,000
Term Loan [Member] | Silicon Valley Bank, Amended And Restated Loan Agreement Effective 2/23/18 [Member] | Prime Rate [Member]
Line of Credit Facility [Line Items]
Basis rate	0.50%
Interest rate	5.00%
Mason Lease [Member] | Letter of Credit [Member]
Line of Credit Facility [Line Items]
Letter of credit outstanding		$ 1,250,000

Indebtedness (Future Maturities

Indebtedness (Future Maturities On Debt And Capital Lease Obligations) (Details) $ in Thousands	Dec. 31, 2018USD ($)
Indebtedness [Abstract]
2,019	$ 5,303
2,020	12,942
2,021	12,947
2,022	12,968
2,023	3,467
2024 and thereafter	11,393
Total payments	59,020
Imputed interest	(6,225)
Net debt obligations, of which $4,433 is current and $48,362 is noncurrent	52,795
Net capital lease obligations, current	4,433
Net capital lease obligations, noncurrent	$ 48,362

Commitments and Contingencies_2

Commitments and Contingencies (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Commitments and Contingencies [Line Items]
Advertising costs	$ 785	$ 900	$ 625
Operating lease rent expense	1,146	850	1,250
Royalty expense	$ 2,715	$ 2,323	$ 1,895
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_3

Commitments and Contingencies (Future Minimum Lease Payments Under Non-cancelable Operating Leases) (Details) $ in Thousands	Dec. 31, 2018USD ($)
Commitments and Contingencies [Abstract]
2,019	$ 1,064
2,020	893
2,021	648
2,022	405
Total	$ 3,010

Revenue (Narrative) (Details)

Revenue (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Revenue	$ 201,630	$ 174,716	$ 155,109
Sales [Member]
Disaggregation of Revenue [Line Items]
Concentration Risk, Percentage	10.80%	13.20%	14.40%
Shipping and Handling [Member]
Disaggregation of Revenue [Line Items]
Revenue	$ 1,236	$ 1,090	$ 1,266

Income Taxes (Narrative) (Detai

Income Taxes (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2017	Dec. 31, 2015
Income Tax Contingency [Line Items]
Federal tax at statutory rate	21.00%	34.00%	34.00%
Net interest expense	$ 3,131,000
Deferred tax asset which full valuation allowance was recorded	774,000
Reduction to federal deferred tax assets	2,482,000	$ 29,480,000
Current federal tax refund	51,000
Research and development credit carryforward	6,206,000	5,339,000
Pre-tax book loss for domestic operations	(13,443,000)	(19,409,000)	$ (27,271,000)
Pre-tax book loss for international operations	(7,468,000)	(7,469,000)	(6,027,000)
Undistributed earnings of foreign subsidiaries	234,000
Unrecognized deferred tax assets			2,816,000	$ 2,816,000
Deferred tax assets tax credit carryforwards research and unrecognized tax benefits reduction from IRS audit	2,018,000
Unrecognized tax benefits that would impact effective tax rate	0	0	0
Unrecognized tax benefits	$ 1,157,000	$ 1,157,000	$ 3,175,000		$ 1,982,000
Tax Year 2014 [Member]
Income Tax Contingency [Line Items]
Open Tax Year	2,014
Tax Year 2015 [Member]
Income Tax Contingency [Line Items]
Open Tax Year	2,015
Federal [Member]
Income Tax Contingency [Line Items]
Operating loss carryforward	$ 18,228,000
Research and development credit carryforward	6,154,000
Federal [Member] | Tax Year 2021 And 2038 [Member]
Income Tax Contingency [Line Items]
Operating loss carryforward	239,162,000
State [Member]
Income Tax Contingency [Line Items]
Operating loss carryforward	154,370,000
Foreign [Member]
Income Tax Contingency [Line Items]
Operating loss carryforward	$ 37,694,000
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, 2023
Minimum [Member] | State [Member]
Income Tax Contingency [Line Items]
Operating loss carryforward, expiration year	Dec. 31, 2019
Minimum [Member] | Foreign [Member]
Income Tax Contingency [Line Items]
Operating loss carryforward, expiration year	Dec. 31, 2019
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, 2039
Maximum [Member] | State [Member]
Income Tax Contingency [Line Items]
Operating loss carryforward, expiration year	Dec. 31, 2039
Maximum [Member] | Foreign [Member]
Income Tax Contingency [Line Items]
Operating loss carryforward, expiration year	Dec. 31, 2028

Income Taxes (Summary Of Detail

Income Taxes (Summary Of Detail Of Deferred Tax Assets And Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets (liabilities):
Net operating loss carryforward	$ 68,563	$ 64,776
Research and development and AMT credit carryforwards, net	6,206	5,339
Deferred interest	774
Equity compensation	4,750	6,955
Accruals and reserves	802	874
Inventories	726	588
Intangible assets	(11,448)	(11,297)
Property and equipment, net	(608)	(339)
Other, net	135	179
Subtotal	69,900	67,075
Less valuation allowance	(69,849)	(66,973)
Total	$ 51	$ 102

Income Taxes (Summary Of Compan

Income Taxes (Summary Of Company's Provision for Income Taxes) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current Tax Expense
Federal	$ (51)
State	28	$ 44	$ 32
Foreign	198	72	8
Total current tax expense	175	116	40
Deferred Tax Expense
Federal	(3,048)	18,485	(7,333)
State	178	(1,337)	210
Foreign	45	(2,241)	(1,177)
Change in valuation allowance	2,876	(15,009)	8,300
Total deferred tax expense	51	(102)
Total tax expense	$ 226	$ 14	$ 40

Income Taxes (Summary Of Differ

Income Taxes (Summary Of Difference Between Effective Income Tax Rates And Federal Statutory Rate) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Taxes [Abstract]
Federal tax at statutory rate	21.00%	34.00%	34.00%
Federal and Foreign tax rate change	(6.84%)	(109.68%)
Federal R&D credit	4.39%	(0.40%)	2.89%
Federal deferred adjustment	(10.77%)
Federal NOL adjustment for ASU		10.48%
Valuation allowance	(13.75%)	55.84%	(24.93%)
State income taxes	(0.99%)	4.81%	(0.69%)
Foreign NOL adjustment	(1.22%)	1.30%	(1.36%)
Foreign tax rate differential	(0.60%)	(2.45%)	(1.62%)
Permanent differences and other	7.70%	6.05%	(8.41%)
Effective tax rate, Total	(1.08%)	(0.05%)	(0.12%)
Federal tax at statutory rate	$ (4,391)	$ (9,139)	$ (11,322)
Federal and Foreign tax rate change	1,430	29,480
Federal deferred adjustment	2,253
Federal R&D credit	(918)	107	(962)
Federal NOL adjustment for ASU		(2,816)
Valuation allowance	2,876	(15,009)	8,300
State income taxes	206	(1,292)	231
Foreign NOL adjustment	256	(348)	452
Foreign tax rate differential	125	658	539
Permanent differences and other	(1,611)	(1,627)	2,802
Total tax expense	$ 226	$ 14	$ 40

Income Taxes (Summary Of Reconc

Income Taxes (Summary Of Reconciliation Of Change In Federal And State Unrecognized Tax Benefits) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Taxes [Abstract]
Balance at the beginning of the year	$ 1,157	$ 3,175	$ 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	$ 1,157	$ 3,175

Concentrations (Narrative) (Det

Concentrations (Narrative) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)customer	Dec. 31, 2017	Dec. 31, 2016
Concentration Risk [Line Items]
Number of customers | customer	10
Cash and cash equivalents balance in excess of FDIC limits | $	$ 31,955
Sales [Member]
Concentration Risk [Line Items]
Percentage representation of significant customer	10.80%	13.20%	14.40%
Customer Concentration Risk [Member] | Accounts Receivable [Member]
Concentration Risk [Line Items]
Percentage representation of significant customer	11.80%	19.70%

Employee Benefit Plans (Narrati

Employee Benefit Plans (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
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	$ 1,560,000	$ 1,367,000	$ 1,222,000
Discretionary contributions made	0	0	0
Total contributions to retirement plan	$ 243,000	$ 205,000	$ 101,000

Equity Compensation Plans (Narr

Equity Compensation Plans (Narrative) (Details) - USD ($) $ / shares in Units, shares in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total intrinsic value of options exercised	$ 5,343,000	$ 5,121,000	$ 3,550,000
Tax benefit recognized	0	0	0
Share-based compensation expense recognized	$ 16,495,000	$ 14,615,000	11,697,000
Time-Based Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average period of recognizing cost	2 years
Options awarded	52	65
Stock options compensation costs	$ 1,432,000
Restricted Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average period of recognizing cost	1 year 6 months
Total fair value of restricted stock vested	$ 11,864,000	$ 6,235,000	5,102,000
Unrecognized compensation costs related to non-vested performance options	$ 18,766,000
Performance options awarded to President and CEO	630	771
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
Weighted average period of recognizing cost	1 year 10 months 24 days
Share-based compensation expense recognized	$ 0	$ 43,000	269,000
Options awarded
Number of shares options vest in	25
Period of considering closing price of common stock	30 days
Stock options compensation costs	$ 1,869,000
Contractual term (years)	10 years
Stock Options And Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation costs related to non-vested share-based compensation arrangements with performance shares	$ 20,198,000
Share-based compensation expense recognized	$ 15,032,000	$ 13,908,000	$ 10,872,000
Performance Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance options awarded to President and CEO	90
President And CEO [Member] | Performance Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options awarded	450
Minimum [Member] | Time-Based Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Contractual term (years)	5 years 1 month 21 days	5 years 2 months 16 days	5 years 3 months 7 days
Expected volatility of stock	41.00%	43.00%	46.00%
Interest rate	2.31%	1.75%	1.06%
Minimum [Member] | Restricted Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	1 year
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] | Time-Based Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Contractual term (years)	5 years 8 months 16 days	5 years 9 months 4 days	7 years 1 month 6 days
Expected volatility of stock	42.00%	48.00%	51.00%
Interest rate	3.01%	2.12%	2.02%
Maximum [Member] | Restricted Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	4 years
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	11,099
Shares available for future grants	1,319
2014 Plan [Member] | Time-Based Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercisable period beginning	3 years
2008 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense recognized	$ 697,000	$ 664,000	$ 556,000
Company's common stock may be purchased at a discount	15.00%
Participants purchase limit value	$ 25,000
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 future issuance under the ESPP	595
2018 PSAs [Member] | Performance Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
2018 PSAs [Member] | Performance Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense recognized	$ 766,000
2018 PSAs [Member] | Minimum [Member] | Performance Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance stock award threshold, target and maximum payout opportunity percentage	0.00%
2018 PSAs [Member] | Maximum [Member] | Performance Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance stock award threshold, target and maximum payout opportunity percentage	200.00%
First Anniversary Date Of Grant [Member] | 2014 Plan [Member] | Time-Based Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual vesting percentage	25.00%
First, Second, And Third Anniversaries [Member] | Stock Options, RSA's, and RSU's [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual vesting percentage	0.33%
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
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
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
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
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

Equity Compensation Plans (Acti

Equity Compensation Plans (Activity Under Stock Based Compensation Plans) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Time-Based Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning balance, Number of Shares Outstanding, Stock Options	2,026	2,454
Granted, Number of Shares Outstanding, Stock Options	52	65
Exercised, Number of Shares Outstanding, Stock Options	(474)	(458)
Cancelled or forfeited, Number of Shares Outstanding, Stock Options	(22)	(35)
Ending balance, Number of Shares Outstanding, Stock Options	1,582	2,026	2,454
Vested and expected to vest, Number of Shares Outstanding, Stock Options	1,574	2,004
Exercisable, Ending balance, Number of Shares Outstanding, Stock Options	1,419	1,766
Beginning balance, Weighted Average Exercise Price, Stock Options	$ 13.30	$ 12.51
Granted, Weighted Average Exercise Price, Stock Options	26.05	20.22
Exercised, Weighted Average Exercise Price, Stock Options	12.70	9.61
Cancelled or forfeited, Weighted Average Exercise Price, Stock Options	18.14	19.08
Ending balance, Weighted Average Exercise Price, Stock Options	13.83	13.30	$ 12.51
Vested and expected to vest, Weighted Average Exercise Price, Stock Options	13.78	13.23
Exercisable, Ending balance, Weighted Average Exercise Price, Stock Options	$ 12.99	$ 12.48
Outstanding, Ending balance, Weighted Average Remaining Contractual Term, Stock Options	5 years 7 days	5 years 7 months 13 days
Vested and expected to vest, Weighted Average Remaining Contractual Term, Stock Options	5 years	5 years 6 months 29 days
Exercisable, Ending balance, Weighted Average Remaining Contractual Term, Stock Options	4 years 7 months 17 days	5 years 2 months 12 days
Outstanding, Ending balance, Aggregate Intrinsic Value, Stock Options	$ 26,587	$ 11,730
Vested and expected to vest, Aggregate Intrinsic Value, Stock Options	26,525	11,717
Exercisable, Ending balance, Aggregate Intrinsic Value, Stock Options	$ 24,991	$ 11,471
Restricted Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning balance, Number of Shares Outstanding	1,845	1,416
Awarded, Number of Shares Outstanding	630	771
Released, Number of Shares Outstanding	(638)	(331)
Forfeited, Number of Shares Outstanding	(91)	(11)
Ending balance, Number of Shares Outstanding	1,746	1,845	1,416
Beginning balance, Weighted Average Grant Date Fair Value	$ 18.22	$ 17.40
Awarded, Weighted Average Grant Date Fair Value	18.71	19.38	$ 16.35
Released, Weighted Average Grant Date Fair Value	18.87	18.52
Forfeited, Weighted Average Grant Date Fair Value	17.97	17.43
Ending balance, Weighted Average Grant Date Fair Value	$ 18.19	$ 18.22	$ 17.40
Performance Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning balance, Number of Shares Outstanding
Awarded, Number of Shares Outstanding	90
Released, Number of Shares Outstanding
Forfeited, Number of Shares Outstanding
Ending balance, Number of Shares Outstanding	90
Beginning balance, Weighted Average Grant Date Fair Value
Awarded, Weighted Average Grant Date Fair Value	17.71
Released, Weighted Average Grant Date Fair Value
Forfeited, Weighted Average Grant Date Fair Value
Ending balance, Weighted Average Grant Date Fair Value	$ 17.71
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	350	250
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	4 years 5 months 12 days	5 years 5 months 12 days
Exercisable, Ending balance, Weighted Average Remaining Contractual Term, Stock Options	4 years 5 months 12 days	5 years 5 months 12 days
Outstanding, Ending balance, Aggregate Intrinsic Value, Stock Options	$ 5,555	$ 2,774
Exercisable, Ending balance, Aggregate Intrinsic Value, Stock Options	$ 4,321	$ 1,541

Equity Compensation Plans (Shar

Equity Compensation Plans (Share-Based Compensation Expense Related to Employee Share-Based Compensation) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total	$ 16,495	$ 14,615	$ 11,697
Cost of Revenue [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total	1,545	610	420
Research and Development Expenses [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total	1,987	2,052	1,825
Selling, General and Administrative Expenses [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total	$ 12,963	$ 11,953	$ 9,452

Equity Compensation Plans (Assu

Equity Compensation Plans (Assumptions Used for Determining Fair Value of Options) (Details) - Time-Based Stock Options [Member]	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average volatility	41.51%	44.50%	48.87%
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	2.31%	1.75%	1.06%
Expected life of option (years)	5 years 1 month 21 days	5 years 2 months 16 days	5 years 3 months 7 days
Expected volatility of stock	41.00%	43.00%	46.00%
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	3.01%	2.12%	2.02%
Expected life of option (years)	5 years 8 months 16 days	5 years 9 months 4 days	7 years 1 month 6 days
Expected volatility of stock	42.00%	48.00%	51.00%

Equity Compensation Plans (Weig

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, 2018	Dec. 31, 2017	Dec. 31, 2016
Time-Based Stock Options [Member]
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	$ 10.97	$ 8.60	$ 8.25
Restricted Stock Awards [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	18.71	$ 19.38	$ 16.35
Performance Stock Awards [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	$ 17.71

Equity Compensation Plans (Esti

Equity Compensation Plans (Estimated Grant Date Fair Value Per Share of Performance Options Granted) (Details) - Performance Stock Options [Member]	12 Months Ended
	Dec. 31, 2018$ / shares
Tranche 1 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Price Target	$ 10
Tranche 2 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Price Target	12.50
Tranche 3 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Price Target	15
Tranche 4 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Price Target	17.50
Tranche 5 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Price Target	20
Tranche 6 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Price Target	25
Tranche 7 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Price Target	30
Tranche 8 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Price Target	35
Tranche 9 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Price Target	40
Fair Value Of 2012 Grant [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] | 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] | 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] | 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] | 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] | 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] | 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] | 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] | 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] | 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] | 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] | 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] | 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] | 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] | 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] | 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] | 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] | Tranche 9 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Fair Value	$ 14.61

Segment and Geographic Inform_3

Segment and Geographic Information (Narrative) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Europe [Member]
Long-lived assets	$ 1,296	$ 957

Segment and Geographic Inform_4

Segment and Geographic Information (Revenue by Geographic Area) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	$ 52,893	$ 49,941	$ 51,802	$ 46,994	$ 46,062	$ 42,150	$ 45,231	$ 41,273	$ 201,630	$ 174,716	$ 155,109
United States [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									162,146	138,387	122,385
Europe [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									25,912	21,901	19,772
Asia [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									12,687	13,616	12,223
Other International [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									885	812	729
International [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									$ 39,484	$ 36,329	$ 32,724

Segment and Geographic Inform_5

Segment and Geographic Information (Revenue by Product Type) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue from External Customer [Line Items]
Revenue	$ 52,893	$ 49,941	$ 51,802	$ 46,994	$ 46,062	$ 42,150	$ 45,231	$ 41,273	$ 201,630	$ 174,716	$ 155,109
United States [Member]
Revenue from External Customer [Line Items]
Revenue									162,146	138,387	122,385
United States [Member] | Open-heart Ablation [Member]
Revenue from External Customer [Line Items]
Revenue									72,250	64,517	58,050
United States [Member] | Minimally Invasive Ablation [Member]
Revenue from External Customer [Line Items]
Revenue									35,053	34,421	31,169
United States [Member] | Appendage Management [Member]
Revenue from External Customer [Line Items]
Revenue									52,891	37,281	30,321
United States [Member] | Ablation And Appendage Management [Member]
Revenue from External Customer [Line Items]
Revenue									160,194	136,219	119,540
United States [Member] | Valve Tools [Member]
Revenue from External Customer [Line Items]
Revenue									1,952	2,168	2,845
International [Member]
Revenue from External Customer [Line Items]
Revenue									39,484	36,329	32,724
International [Member] | Open-heart Ablation [Member]
Revenue from External Customer [Line Items]
Revenue									21,118	20,718	20,189
International [Member] | Minimally Invasive Ablation [Member]
Revenue from External Customer [Line Items]
Revenue									9,176	8,007	8,065
International [Member] | Appendage Management [Member]
Revenue from External Customer [Line Items]
Revenue									8,988	7,251	3,986
International [Member] | Ablation And Appendage Management [Member]
Revenue from External Customer [Line Items]
Revenue									39,282	35,976	32,240
International [Member] | Valve Tools [Member]
Revenue from External Customer [Line Items]
Revenue									$ 202	$ 353	$ 484

Selected Quarterly Financial _3

Selected Quarterly Financial Data (Schedule Of Quarterly Financial Information) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating Results:
Revenue	$ 52,893	$ 49,941	$ 51,802	$ 46,994	$ 46,062	$ 42,150	$ 45,231	$ 41,273	$ 201,630	$ 174,716	$ 155,109
Gross profit	38,590	35,948	38,079	34,503	32,683	30,918	32,554	30,008	147,120	126,163	111,101
Income (loss) from operations	(2,607)	(6,048)	958	(9,430)	(2,135)	(6,847)	(6,355)	(9,642)	(17,127)	(24,979)	(31,138)
Net loss	$ (3,430)	$ (7,235)	$ (338)	$ (10,134)	$ (2,580)	$ (7,246)	$ (6,883)	$ (10,183)	$ (21,137)	$ (26,892)	$ (33,338)
Net loss per share (basic and diluted)	$ (0.09)	$ (0.22)	$ (0.01)	$ (0.31)	$ (0.08)	$ (0.22)	$ (0.21)	$ (0.32)

Schedule II (Schedule Of Valuat

Schedule II (Schedule Of Valuation And Qualifying Accounts) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Sales Returns and Allowances [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	$ 1,169	$ 834	$ 207
Additions	312	441	634
Deductions	71	106	7
Ending Balance	1,410	1,169	834
Allowance For Inventory Valuation [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	889	1,080	843
Additions	718	1,004	1,692
Deductions	578	1,195	1,455
Ending Balance	1,029	889	1,080
Valuation Allowance For Deferred Tax Assets [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	66,973	81,982	73,682
Additions	2,876		8,300
Deductions		15,009
Ending Balance	$ 69,849	$ 66,973	$ 81,982