AtriCure (ATRC) 10-K24 Feb 202019 FY Annual reportFinancial data

Company Profile

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2019	Feb. 20, 2020	Jun. 30, 2019
Document And Entity Information [Abstract]
Document Type	10-K
Document Annual Report	true
Current Fiscal Year End Date	--12-31
Document Period End Date	Dec. 31, 2019
Document Transition Report	false
Entity File Number	000-51470
Entity Registrant Name	AtriCure, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	34-1940305
Entity Address, Address Line One	7555 Innovation Way
Entity Address, City or Town	Mason
Entity Address, State or Province	OH
Entity Address, Postal Zip Code	45040
City Area Code	513
Local Phone Number	755-4100
Title of 12(b) Security	Common Stock, $.001 par value
Trading Symbol	ATRC
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Public Float			$ 1,110.6
Entity Common Stock, Shares Outstanding		40,048,972
Documents Incorporated By Reference	DOCUMENTS INCORPORATED BY REFERENCE Items 10, 11, 12, 13 and 14 of Part III of this Form 10-K incorporate information by reference from the registrant’s definitive proxy statement to be filed with the Securities and Exchange Commission within 120 days after the end of the fiscal year covered by this Form 10-K.
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Central Index Key	0001323885

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 28,483	$ 32,231
Short-term investments	53,318	92,171
Accounts receivable, less allowance for doubtful accounts of $1,124 and $547	28,046	25,195
Inventories	29,414	22,484
Prepaid and other current assets	3,899	2,592
Total current assets	143,160	174,673
Property and equipment, net	32,646	27,080
Operating lease right-of-use assets	4,032
Long-term investments	12,675
Intangible assets, net	129,881	49,254
Goodwill	234,781	105,257
Other noncurrent assets	705	495
Total Assets	557,880	356,759
Current liabilities:
Accounts payable	14,948	9,659
Accrued liabilities	32,750	25,840
Other current liabilities and current maturities of leases and long-term debt	2,218	4,717
Total current liabilities	49,916	40,216
Long-term debt	59,634	35,571
Finance lease liabilities	11,774	12,172
Operating lease liabilities	2,796
Other noncurrent liabilities	186,417	19,419
Total Liabilities	310,537	107,378
Commitments and contingencies (Note 12)
Stockholders' Equity:
Common stock, $0.001 par value, 90,000 shares authorized and 39,655 and 38,604 issued and outstanding	40	39
Additional paid-in capital	529,658	496,544
Accumulated other comprehensive loss	(158)	(199)
Accumulated deficit	(282,197)	(247,003)
Total Stockholders' Equity	247,343	249,381
Total Liabilities and Stockholders' Equity	$ 557,880	$ 356,759

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Consolidated Balance Sheets [Abstract]
Accounts receivable, allowance for doubtful accounts	$ 1,124	$ 547
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	90,000,000	90,000,000
Common stock, shares issued	39,655,000	38,604,000
Common stock, shares outstanding	39,655,000	38,604,000

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Consolidated Statements of Operations and Comprehensive Loss [Abstract]
Revenue	$ 230,807	$ 201,630	$ 174,716
Cost of revenue	60,472	54,510	48,553
Gross profit	170,335	147,120	126,163
Operating expenses:
Research and development expenses	41,230	34,723	34,144
Selling, general and administrative expenses	162,227	129,524	116,998
Total operating expenses	203,457	164,247	151,142
Loss from operations	(33,122)	(17,127)	(24,979)
Other income (expense):
Interest expense	(4,111)	(4,607)	(2,264)
Interest income	2,398	1,006	227
Other	(160)	(183)	138
Loss before income tax expense	(34,995)	(20,911)	(26,878)
Income tax expense	199	226	14
Net loss	$ (35,194)	$ (21,137)	$ (26,892)
Basic and diluted net loss per share	$ (0.94)	$ (0.62)	$ (0.83)
Weighted average shares outstanding — basic and diluted	37,589	34,087	32,387
Comprehensive loss:
Unrealized gain (loss) on investments	$ 137	$ (31)	$ 15
Foreign currency translation adjustment	(96)	(202)	487
Other comprehensive income (loss)	41	(233)	502
Net loss	(35,194)	(21,137)	(26,892)
Comprehensive loss, net of tax	$ (35,153)	$ (21,370)	$ (26,390)

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, 2016	$ 33	$ 367,851	$ (198,974)	$ (468)	$ 168,442
Beginning 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
Issuance of common stock for SentreHEART acquisition	$ 1	20,306			20,307
Issuance of common stock for SentreHEART acquisition, Shares	699
Issuance of common stock under equity incentive plans		(7,831)			(7,831)
Issuance of common stock under equity incentive plans, Shares	248
Issuance of common stock under employee stock purchase plan		2,662			2,662
Issuance of common stock under employee stock purchase plan, Shares	104
Share-based employee compensation expense		17,977			17,977
Other comprehensive income (loss)				41	41
Net loss			(35,194)		(35,194)
Ending Balance at Dec. 31, 2019	$ 40	$ 529,658	$ (282,197)	$ (158)	$ 247,343
Ending Balance, Shares at Dec. 31, 2019	39,655

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities:
Net loss	$ (35,194)	$ (21,137)	$ (26,892)
Adjustments to reconcile net loss to net cash used in operating activities:
Share-based compensation expense	17,977	16,495	14,615
Depreciation	7,423	7,244	7,761
Amortization of intangible assets	1,943	1,510	1,367
Amortization of deferred financing costs	375	515	264
Non-cash lease expense	751
Loss on disposal of property and equipment and impairment of assets	604	323	336
Realized loss (gain) from foreign exchange on intercompany transactions	181	165	(173)
(Accretion) amortization of investments	(922)	(362)	30
Provision for doubtful accounts	582	598	(172)
Change in fair value of contingent consideration	(4,916)	(10,825)	(4,078)
Payment of contingent consideration in excess of purchase accounting amount		(96)
Changes in operating assets and liabilities, net of amounts acquired:
Accounts receivable	(3,201)	(2,837)	(1,464)
Inventories	(5,151)	(146)	(4,477)
Other current assets	(1,199)	(367)	829
Accounts payable	2,790	(2,398)	1,290
Accrued liabilities	3,108	7,016	2,228
Other noncurrent assets and liabilities	(962)	131	(408)
Net cash used in operating activities	(15,811)	(4,171)	(8,944)
Cash flows from investing activities:
Purchases of available-for-sale securities	(73,249)	(106,588)	(16,455)
Sales and maturities of available-for-sale securities	100,485	27,389	26,600
Purchases of property and equipment	(12,182)	(6,211)	(6,384)
Proceeds from sale of property and equipment	39	6
Cash paid for business combination	(17,240)
Net cash (used in) provided by investing activities	(2,147)	(85,404)	3,761
Cash flows from financing activities:
Proceeds from sale of stock, net of offering costs of $229		82,873
Proceeds from debt borrowings	20,000	17,381
Payments of debt and finance leases	(629)	(1,755)	(1,689)
Payment of debt fees	(329)	(1,136)	(50)
Proceeds from stock option exercises	1,202	6,012	4,402
Shares repurchased for payment of taxes on stock awards	(9,033)	(4,457)	(2,013)
Proceeds from issuance of common stock under employee stock purchase plan	2,662	2,383	2,110
Payment of contingent consideration liability previously established in purchase accounting		(1,125)
Proceeds from economic incentive loan	500
Net cash provided by financing activities	14,373	100,176	2,760
Effect of exchange rate changes on cash and cash equivalents	(163)	(179)	24
Net (decrease) increase in cash and cash equivalents	(3,748)	10,422	(2,399)
Cash and cash equivalents-beginning of period	32,231	21,809	24,208
Cash and cash equivalents-end of period	28,483	32,231	21,809
Supplemental cash flow information:
Cash paid for interest	3,719	3,870	2,002
Cash paid for income taxes	259	65	37
Non-cash investing and financing activities:
Contingent consideration in business combinations	171,300
Stock issuance in business combinations	20,307
Share-settled portion of contingent consideration		6,279
Accrued purchases of property and equipment	1,053	348	650
Assets obtained in exchange for finance lease obligations	$ 270	24	$ 2
Finance lease early termination		$ (6)

Consolidated Statements of Ca_2

Consolidated Statements of Cash Flows (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)
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, 2019
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 AtriCure, Inc. and our wholly-owned subsidiaries. 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 purchase as cash equivalents. Cash equivalents include demand deposits, money market funds and repurchase agreements on deposit with certain financial institutions. Investments— The Company makes 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 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 13 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 using the expected value method 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, 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 expenses. The Company 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 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. Inventory reserves for excess, obsolete and expired products are impacted by uncertain timing of regulatory approvals, variability in product launch strategies and variation in product use. 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 8). The Company reassesses the useful lives of property and equipment at least 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 at least annually 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 technologies which have 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. The IPR&D assets represent estimates of the fair value of the pre-market approval (PMA) that may result from the CONVERGE IDE and aMAZE IDE clinical trials. The Company reviews intangible assets for impairment using its best estimates based on reasonable and supportable assumptions and projections of expected future cash flows. The Company performs impairment testing annually on October 1. If the IPR&D project is abandoned or regulatory approvals are not obtained, we may have a full or partial impairment charge related to the IPR&D, calculated as the excess carrying value of the IPR&D assets over the estimated fair value. 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 tests goodwill for impairment annually on October 1, or more often if impairment indicators are present. Contingent Consideration and other Noncurrent Liabilities— This balance consists of the contingent consideration recorded in business combinations, as well as deferred revenues, asset retirement obligations and other contractual obligations. The 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 and SentreHEART merger agreement. Other Income (Expense)— Other income (expense) consists of foreign currency transaction gains and losses generated by settlements of intercompany balances denominated in Euros and invoices transacted in British Pounds. Taxes — Deferred income tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases and operating loss and tax credit carryforwards. Deferred income tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred income tax assets and liabilities from a change in tax rates is recognized in the period that includes the enactment date. The Company’s estimate of the valuation allowance for deferred income tax assets requires significant estimates and judgments about 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 the deferred income tax asset will not be realized. Significant weight is given to evidence that can be objectively verified. The Company evaluates deferred income tax assets on an annual basis to determine if valuation allowances are required. 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, and tax planning strategies that are both prudent and feasible. In evaluating the need for a valuation allowance, 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. The Tax Cut and Jobs Act (Tax Reform Act) allows companies an election to reclassify the income tax effects of the Tax Reform Act on items within accumulated other comprehensive income (loss) to retained earnings. The Company has not made this election due to its full valuation allowance. Net Loss Per Share— Basic and diluted net loss per share is computed 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 3,623 , 3,869 and 4,321 stock options, restricted stock awards, restricted stock units and performance share awards as of December 31, 2019, 2018 and 2017 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): 2019 2018 2017 Total accumulated other comprehensive (loss) income at beginning of period $ ( 199 ) $ 34 $ ( 468 ) Unrealized gains (losses) on investments Balance at beginning of period $ ( 37 ) $ ( 6 ) $ ( 21 ) Other comprehensive income (loss) before reclassifications 137 ( 31 ) 15 Amounts reclassified from accumulated other comprehensive (loss) income to other income — — — Balance at end of period $ 100 $ ( 37 ) $ ( 6 ) Foreign currency translation adjustment Balance at beginning of period $ ( 162 ) $ 40 $ ( 447 ) Other comprehensive (loss) income before reclassifications ( 277 ) ( 367 ) 660 Amounts reclassified from accumulated other comprehensive (loss) income to other income 181 165 ( 173 ) Balance at end of period $ ( 258 ) $ ( 162 ) $ 40 Total accumulated other comprehensive (loss) income at end of period $ ( 158 ) $ ( 199 ) $ 34 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 $ 635 , $ 785 and $ 900 during the years ended December 31, 2019, 2018 and 2017. Share-Based Compensation— The Company records 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. The Company estimates the fair value of share-based payment awards on the date of grant. 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 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 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 estimated fair value of performance share awards may be adjusted over the performance period based on changes to estimates of performance target achievement. 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, repurchase agreements, 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 measurements of the Level 3 contingent consideration liabilities 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
Recent Accounting Pronouncements	Dec. 31, 2019
Recent Accounting Pronouncements [Abstract]
Recent Accounting Pronouncements	2. RECENT ACCOUNTING PRONOUNCEMENTS In June 2016, the FASB issued ASU 2016-13, “Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments” (ASU 2016-13). This guidance requires that financial assets measured at amortized costs, such as trade receivables and contract assets, be presented net of expected credit losses, which may be estimated based on relevant information such as historical experience, current conditions and future expectations for each pool of similar financial assets. The new guidance requires enhanced disclosures related to the trade receivables and associated credit losses. The guidance is effective for interim and annual periods beginning within 2020. The adoption of this guidance is expected to increase the level of disclosures related to the Company’s trade receivables, however it is not expected to have a material impact on the Company’s consolidated financial statements. 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 interim and annual periods beginning within 2020, with early adoption permitted, and applied prospectively. The Company does not expect the adoption of this standard to have a material impact on its consolidated financial statements. 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 has elected to early adopt the guidance, and the fair value measurement disclosures herein reflect the adoption of the provisions of ASU 2018-13 as of December 31, 2019. 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). The guidance in ASC 350-40 on internal-use software is applied 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 operations and comprehensive loss as that in which the fee associated with the hosting arrangement is presented. The amendments are effective for interim and annual reporting periods beginning within 2020, with early adoption permitted. During 2019, the Company adopted this standard prospectively, and has deferred eligible costs related to implementation of hosting arrangements within other current and noncurrent assets. These costs are amortized in the same income statement line as the associated hosting subscription fees and operating expenses. The adoption of ASU 2018-15 did not have a material impact on the Company’s consolidated financial statements. In December 2019, the FASB issued ASU 2019-12, “Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes” (2019-12). The amendment simplifies the accounting for income taxes by eliminating some exceptions to the general approach in ASC 740, Income Taxes. It also clarifies certain aspects of the existing guidance to promote more consistent application, among other things. The guidance is effective for interim and annual reporting periods beginning within 2021 with early adoption permitted. The Company has elected to early adopt the simplification guidance, and there is no impact on prior periods.

Fair Value

Fair Value	12 Months Ended
Fair Value	Dec. 31, 2019
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, 2019: 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 $ — $ 14,502 $ — $ 14,502 Repurchase agreements — 10,000 — 10,000 Commercial paper — 13,755 — 13,755 U.S. government agencies and securities 8,539 — — 8,539 Corporate bonds — 24,852 — 24,852 Asset-backed securities — 18,847 — 18,847 Total assets $ 8,539 $ 81,956 $ — $ 90,495 Liabilities: Acquisition-related contingent consideration $ — $ — $ 185,157 $ 185,157 Total liabilities $ — $ — $ 185,157 $ 185,157 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 There were no changes in the levels or methodology of measurement of financial assets and liabilities during the years ended December 31, 2019 and 2018. Acquisition-Related Contingent Consideration. The Company has contingent consideration arrangements arising from the nContact and SentreHEART acquisitions. Contingent consideration arrangements under the nContact merger agreement obligate the Company to pay former shareholders of nContact for the following milestones, if achieved:  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.  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.  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 2019 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 and an additional 232 shares were issued upon completion of the trial enrollment milestone in 2018. Contingent consideration arrangements under the SentreHEART merger agreement obligate the Company to pay certain defined amounts to former shareholders of SentreHEART if specified milestones are met related to the aMAZE IDE clinical trial, including PMA approval, and reimbursement for the therapy involving SentreHEART’s devices. In connection with the acquisition of SentreHEART on August 13, 2019, preliminary fair value of $ 171,300 was recorded for the SentreHEART contingent consideration. See Note 5 for more details regarding the SentreHEART acquisition-related contingent consideration. Subject to the terms and conditions of the SentreHEART merger agreement, all contingent consideration would be paid in cash and stock at the discretion of the Company, subject to certain limitations, with the maximum number of shares that may be issued after closing limited to 7,021 , of which 699 shares were issued at closing of the SentreHEART acquisition on August 13, 2019. The maximum contingent consideration payable by AtriCure will not exceed $ 260,000 . 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 and projected revenues, 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 recurring Level 3 fair value measurements of the contingent consideration liabilities include the following significant inputs as of December 31, 2019: Weighted average Fair Value Valuation Technique Input Range by relative fair value Discount rate 5.56 % 5.56 % Regulatory & Commercialization-based milestones $ 185,157 Probability-weighted scenario approach Projected month and year of payment June 2020 - September 2025 n/a Probability of payment 77.40 - 85.00 % 81.75 % Contingent consideration liabilities are periodically remeasured. Changes in the discount rate, time until payment and probabilities of payment may result in materially different fair value measurements. A decrease in the discount rate would result in a higher fair value measurement, while a decrease in the probability of payment would result in a lower fair value measurement. Movement in the forecasted timing of achievement to later in the milestone periods also causes a decrease in the fair value measurement. Subsequent revisions in 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 2019, resulting in a decrease in fair value due to actual 2019 revenues falling below the commercial milestone target and changes in estimates related to the forecasted timing of achievement of the nContact regulatory milestone. The fair value of the SentreHEART contingent consideration was remeasured during 2019 resulting in an increase in fair value due to accretion and changes in the discount rate. 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: 2019 2018 2017 Beginning Balance – January 1 $ 18,773 $ 37,098 $ 41,176 Amounts acquired 171,300 — — Settlement of trial enrollment milestone — ( 7,500 ) — Changes in fair value included in selling, general and administrative expenses ( 4,916 ) ( 10,825 ) ( 4,078 ) Ending Balance – December 31 $ 185,157 $ 18,773 $ 37,098

Investments

Investments	12 Months Ended
Investments	Dec. 31, 2019
Investments [Abstract]
Investments	4. INVESTMENTS Investments as of December 31, 2019 consisted of the following: Unrealized Gains Cost Basis (Losses) Fair Value Corporate bonds $ 24,796 $ 56 $ 24,852 U.S. government agencies and securities 8,529 10 8,539 Commercial paper 13,755 — 13,755 Asset-backed securities 18,813 34 18,847 Total $ 65,893 $ 100 $ 65,993 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 The Company has no t experienced any significant realized gains or losses on its investments in the years ended December 31, 2019, 2018 and 2017.

Business Combinations

Business Combinations	12 Months Ended
Business Combinations	Dec. 31, 2019
Business Combinations [Abstract]
Business Combinations	5. BUSINESS COMBINATIONS On August 13, 2019, the Company acquired 100 % of the outstanding equity interests of SentreHEART. Founded in 2005 and based in Redwood City, California, SentreHEART developed innovative technology for remote delivery of a suture for closure of anatomic structures including the left atrial appendage (LAA). This technology is currently being studied in the aMAZE IDE clinical trial, an FDA-approved, prospective, multicenter, randomized controlled trial. The objective of the aMAZE Trial is to demonstrate that the LARIAT ® device for LAA closure, plus a Pulmonary Vein Isolation (PVI) ablation, will lead to a reduced incidence of recurrent Afib compared to PVI alone. Management believes the acquisition of SentreHEART will significantly expand the Company’s addressable markets with a product designed for electrophysiologists, and the acquisition of SentreHEART deepens the Company’s commitment to provide the broadest possible offering of ablation and LAA management solutions to patients and customers. The total consideration paid to SentreHEART’s former shareholders at the acquisition date was $ 18,008 in cash and 699 shares of AtriCure common stock valued at approximately $ 20,307 . The cash paid at acquisition was subject to adjustment for net working capital balances outside of a specified range, resulting in $ 768 adjustment paid to the Company in November 2019. The merger agreement also provides for the Company to pay contingent consideration, as follows:  PMA Milestone – up to $ 140,000 upon receiving PMA from FDA for the LARIAT system with an approved indication allowing commercial distribution in the United States for the closure of the LAA for treatment of atrial fibrillation. The full contingent consideration amount is only received if PMA approval is received on or before December 31, 2022 . The potential contingent consideration is reduced by 4.17 % (or one-twenty-fourth) each month following December 2022 and is reduced to zero if the milestone is achieved after December 31, 2023 . Payment of $ 25,000 of the PMA milestone may be accelerated upon achievement of an Interim Success Milestone as defined by the merger agreement.  CPT Reimbursement Milestone – up to $ 120,000 upon approval of a Medicare Category 1 Current Procedural Terminology (CPT) Code by the American Medical Association. The full contingent consideration amount is only received if approval of the CPT Code is received on or before December 31, 2025 . The potential contingent consideration is reduced by 4.17 % (or one-twenty-fourth) each month following December 2025 and is reduced to zero if the milestone is achieved after December 31, 2026 . Subject to the terms and conditions of the merger agreement, all contingent consideration would be paid in cash and stock at the discretion of the Company, subject to certain limitations, with the maximum number of shares that may be issued after closing limited to 7,021 , of which 699 were paid at closing. The maximum contingent consideration payable by AtriCure will not exceed $ 260,000 . The Company accounted for the acquisition in accordance with ASC 805, “Accounting for Business Combinations”. The assets acquired, liabilities assumed and the estimated contingent consideration obligations are recorded at their respective fair values as of the date of acquisition. The process of estimating fair values of identifiable assets, certain intangible assets and assumed liabilities requires significant assumptions and estimates. The judgments used to determine the estimated fair value assigned to each class of assets acquired and liabilities assumed, as well as asset lives, can materially impact the amounts recorded and the Company’s results of operations. The components of the aggregate purchase price for the SentreHEART acquisition are as follows: Fair value of AtriCure common stock issued at closing $ 20,307 Cash 17,240 Fair value of contingent consideration liabilities 171,300 Total purchase price $ 208,847 The fair value of the contingent consideration liabilities was determined by applying the probability-weighted scenario method. Key assumptions in the valuation of the contingent consideration liabilities are based on management’s judgment and estimates and include the probability of achievement of each of the milestones, timing of achievement and discount rates, reflecting the inherent risks of achieving the respective milestones. Some assumptions are not observable in the market, and thus represent a Level 3 measurement within the fair value hierarchy. See Note 3 for disclosure of unobservable inputs. The following table summarizes the estimated fair values of the assets acquired and the liabilities assumed based on the information that was available as of the acquisition date: August 13, 2019 Inventories $ 1,848 Current assets 328 Operating lease right-of-use asset 2,929 Property and equipment 94 Intangible assets 82,570 Other assets 202 Total identifiable assets $ 87,971 Current liabilities $ 5,719 Operating lease liability 2,929 Total liabilities assumed $ 8,648 Net identifiable assets acquired $ 79,323 Goodwill 129,524 Total consideration $ 208,847 During the measurement period, the Company recorded adjustments for the fair value of consideration transferred, including settlement of working capital, and the evaluation of certain tax attributes. As of December 31, 2019, the purchase price allocation has not yet been finalized as the Company evaluates certain tax attributes of SentreHEART. Net deferred tax assets of $ 20,590 and offsetting valuation allowances were also recognized at the acquisition date for the future tax consequences attributable to differences between the above financial statement carrying amounts of existing assets and liabilities and their respective tax bases and acquired operating loss and tax credit carryforwards of SentreHEART. At acquisition, SentreHEART had approximately $ 184,036 of federal and state net operating loss carryforwards, which begin to expire in 2026 and $ 37,906 of federal net operating loss carryforwards which have no expiration as a result of the Tax Reform Act. A portion of the net operating loss carryforwards are subject to certain limitations under Internal Revenue Code Section 382. The Company recorded a full valuation allowance against the net deferred tax assets at acquisition. The goodwill recorded is not deductible for tax purposes. The valuation of the intangible assets acquired and related amortization periods are as follows: Amortization Term Valuation (in years) Developed technology $ 270 15 IPR&D 82,300 Indefinite Total $ 82,570 The fair value of the LARIAT developed technology was estimated using the relief-from-royalty method, an income approach. The LARIAT developed technology asset is amortized on a straight-line basis over its estimated useful life. The IPR&D asset was estimated using the excess earnings method, also an income approach. The IPR&D asset represents an estimate of the fair value of the PMA approval from the in-process aMAZE IDE clinical trial and is accounted for as an indefinite-lived intangible asset until completion or abandonment of the project. The Company recorded the excess of the aggregate purchase price over the estimated fair values of the identifiable net assets acquired as goodwill. Goodwill is primarily attributable to the benefits the Company expects to realize by enhancing its product offering and addressable markets, thereby contributing to an expanded revenue base. As discussed in Note 1, the Company accounts for goodwill in a single reporting unit representing the Company as a whole. The operating results of SentreHEART, including $ 1,280 of appendage management revenue and $ 8,505 of net loss, are included in the Consolidated Statements of Operations and Comprehensive Loss beginning August 14, 2019. The Consolidated Balance Sheet as of December 31, 2019 reflects the acquisition of SentreHEART. The Company recognized approximately $ 3,978 of acquisition-related costs in the year ended December 31, 2019, consisting of legal, audit, tax and other due diligence expenses. Acquisition-related costs are included in selling, general and administrative expenses. The following supplemental pro forma information presents the financial results of the Company for the twelve months ended December 31, 2019 and 2018 as if the acquisition of SentreHEART had occurred on January 1, 2018. Year Ended December 31, (unaudited) 2019 2018 Revenue $ 232,768 $ 205,725 Net loss ( 40,970 ) ( 42,959 ) Basic and diluted net loss per share $ ( 1.09 ) $ ( 1.23 ) Certain pro forma adjustments have been made when calculating the amounts above to reflect the impact of the purchase transaction, primarily consisting of the exclusion of SentreHEART’s interest expense incurred on debt paid off or converted to equity in the acquisition, exclusion of fair value adjustments for SentreHEART’s derivative liabilities and preferred warrants settled as part of the acquisition, adjustments for amortization of intangible assets with determinable lives and exclusion of contingent consideration remeasurement. The Company also eliminated transaction expenses incurred by both AtriCure and SentreHEART. The supplemental pro forma information has been prepared for comparative purposes and does not purport to be indicative of what would have occurred had the acquisition been made on January 1, 2018, nor is it indicative of any future results. The pro forma information does not include any adjustments for potential revenue enhancements, cost synergies or other operating efficiencies that could result from the acquisition.

Intangible Assets And Goodwill

Intangible Assets And Goodwill	12 Months Ended
Intangible Assets And Goodwill	Dec. 31, 2019
Intangible Assets And Goodwill [Abstract]
Intangible Assets And Goodwill	6. INTANGIBLE ASSETS AND GOODWILL The following table provides a summary of the Company’s intangible assets at December 31: 2019 2018 Estimated Accumulated Accumulated Useful Life Cost Amortization Cost Amortization Technology 3 - 15 years $ 11,691 $ 8,131 $ 12,250 $ 7,017 IPR&D 126,321 — 44,021 — Total $ 138,012 $ 8,131 $ 56,271 $ 7,017 Amortization expense related to intangible assets with definite lives, which excludes the IPR&D asset, was $ 1,943 , $ 1,510 and $ 1,367 for the years ended December 31, 2019, 2018 and 2017. 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 was applied prospectively. Future amortization expense is projected as follows: 2020 $ 1,822 2021 1,511 2022 18 2023 18 2024 18 2025 and thereafter 173 Total $ 3,560 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, 2017 $ 105,257 Additions — Net carrying amount as of December 31, 2018 105,257 Additions 129,524 Net carrying amount as of December 31, 2019 $ 234,781

Inventories

Inventories	12 Months Ended
Inventories	Dec. 31, 2019
Inventories [Abstract]
Inventories	7. INVENTORIES Inventories consisted of the following at December 31: 2019 2018 Raw materials $ 11,126 $ 9,100 Work in process 1,260 1,232 Finished goods 17,028 12,152 Inventories $ 29,414 $ 22,484

Property and Equipment

Property and Equipment	12 Months Ended
Property and Equipment	Dec. 31, 2019
Property and Equipment [Abstract]
Property and Equipment	8. PROPERTY AND EQUIPMENT Property and equipment consisted of the following at December 31: Estimated Useful Life 2019 2018 Generators and other capital equipment 1 - 3 years $ 20,167 $ 18,158 Building under finance lease 15 years 14,250 14,250 Computer and other office equipment 3 years 7,606 6,360 Machinery, equipment and vehicles 3 - 7 years 5,905 4,859 Furniture and fixtures 3 - 7 years 5,009 4,702 Leasehold improvements 5 - 15 years 6,078 3,943 Construction in progress N/A 5,708 1,868 Land N/A 502 — Equipment under finance leases 3 - 5 years 483 213 Total 65,708 54,353 Less accumulated depreciation ( 33,062 ) ( 27,273 ) Property and equipment, net $ 32,646 $ 27,080 Property and equipment depreciation expense was $ 7,423 , $ 7,244 and $ 7,761 for the years ended December 31, 2019, 2018 and 2017. Depreciation related to generators and other capital equipment was $ 2,910 , $ 3,191 and $ 3,574 for the years ended 2019, 2018 and 2017. As of December 31, 2019 and 2018, the net carrying value of generators and other capital equipment was $ 4,272 and $ 4,545 .

Accrued Liabilities

Accrued Liabilities	12 Months Ended
Accrued Liabilities	Dec. 31, 2019
Accrued Liabilities [Abstract]
Accrued Liabilities	9. ACCRUED LIABILITIES Accrued liabilities consisted of the following at December 31: 2019 2018 Accrued bonus $ 10,840 $ 9,100 Accrued commissions 8,734 8,065 Accrued payroll and employee-related expenses 6,748 4,512 Sales returns and allowances 3,979 1,410 Other accrued liabilities 59 1,205 Accrued taxes and value-added taxes payable 1,658 886 Accrued royalties 732 662 Total $ 32,750 $ 25,840

Indebtedness

Indebtedness	12 Months Ended
Indebtedness	Dec. 31, 2019
Indebtedness [Abstract]
Indebtedness	10. INDEBTEDNESS Credit Facility. The Company has a Loan and Security Agreement (Loan Agreement) with Silicon Valley Bank (SVB). The Loan Agreement originally effective February 23, 2018 and modified December 28, 2018 was further modified and amended on August 12, 2019 in connection with the SentreHEART acquisition. The Loan Agreement includes a $ 60,000 term loan and $ 20,000 revolving line of credit; however the total combined term loan and revolving line of credit outstanding under the Loan Agreement cannot exceed $ 70,000 at any time prior to SVB’s consent. The term loan and revolving credit facility both mature or expire, as applicable, on August 1, 2024 . Principal payments of the term loan are to be made ratably commencing March 1, 2021 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 or 5.00 %, plus 0.75 % and is subject to an additional 3.00% fee on the $60,000 term loan principal payable at maturity or upon acceleration or prepayment of the term loan. The Company is accruing the 3.00 % fee over the term of the Loan Agreement, with $ 135 accrued in the outstanding loan balance as of December 31, 2019. Additionally, the original financing costs related to the term loan of $ 501 are netted against the outstanding loan balance in the Consolidated Balance Sheets and amortized ratably over the term of the Loan Agreement. The August 2019 refinancing was treated as a debt modification. The revolving line of credit is subject to an annual facility fee of 0.15 % of the revolving line of credit, and any borrowings thereunder bear interest at the greater of the Prime Rate or 5.00 %. 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. The borrowing availability is also limited to allow total debt outstanding under the Loan Agreement to not exceed $ 70,000 at any time prior to SVB’s consent and further reduced by outstanding letters of credit (as specified). As of December 31, 2019, the Company had no borrowings under the revolving credit facility and had borrowing availability of $ 8,750 . 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, 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. Future principal payments of long-term debt are projected as follows: 2020 $ — 2021 14,634 2022 17,561 2023 17,561 2024 10,244 Total long-term debt, of which $ 60,000 is noncurrent $ 60,000

Leases

Leases	12 Months Ended
Leases	Dec. 31, 2019
Leases [Abstract]
Leases	11. LEASES The Company adopted the new lease guidance on January 1, 2019 using the transition method provided by ASU 2018-11, “Leases (Topic 842): Targeted Improvements”. Under this method, the Company has applied the new requirements to leases that existed as of January 1, 2019, rather than at the earliest comparative period presented in the financial statements. Prior periods are presented under legacy ASC 840 lease guidance. As a result of the adoption, the Company recorded operating right-of-use assets and operating lease liabilities of approximately $ 1,884 and $ 2,189 as of January 1, 2019. The difference between the initial operating right-of-use asset and operating lease liability of $ 305 is accrued rent previously recognized under ASC 840. The Company has operating and finance leases for corporate offices, manufacturing and warehouse facilities and computer equipment. The Company has applied the practical expedient and does not separate lease components from nonlease components. The Company has applied the short-term lease recognition exemption and recognizes lease payments in profit or loss for leases that have a lease term of twelve months or less at commencement and do not include a renewal option whose exercise is reasonably certain. Short term lease expense is not significant during the twelve months ended December 31, 2019. The Company’s leases have remaining lease terms of one year to eleven years . Except for the operating lease acquired as part of the SentreHEART acquisition, options to renew or extend leases beyond their initial term have been excluded from measurement of the ROU assets and lease liabilities as exercise is not reasonably certain. The weighted average remaining lease term for operating leases and finance leases is 3.5 years and 11.0 years as of December 31, 2019. The weighted average discount rate used to measure the outstanding operating lease liabilities and finance lease liabilities is 5.9 % and 7.0 % as of December 31, 2019. In connection with the terms of the Company’s corporate headquarters lease, a letter of credit for $ 1,250 was issued to the building lessor in October 2015. The letter of credit is renewed annually and remains outstanding as of December 31, 2019. The components of lease expense are as follows: Twelve Months Ended December 31, 2019 Operating lease cost $ 952 Finance lease cost: Amortization of right-of-use assets 998 Interest on lease liabilities 872 Total finance lease cost $ 1,870 Supplemental cash flow information related to leases is as follows: Twelve Months Ended December 31, 2019 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from operating leases $ 1,026 Operating cash flows from finance leases 872 Financing cash flows from finance leases 629 Right-of-use assets obtained in exchange for lease obligations: Operating Leases 1,884 Finance Leases 270 Operating lease right-of-use asset obtained in business combination 2,929 Supplemental balance sheet information related to leases is as follows: December 31, 2019 Operating Leases Operating lease right-of-use assets $ 4,032 Other current liabilities and current maturities of leases and long-term debt ( 1,465 ) Operating lease liabilities ( 2,796 ) Total operating lease liabilities $ ( 4,261 ) Finance Leases Property and equipment, at cost $ 14,733 Accumulated depreciation ( 4,197 ) Property and equipment, net $ 10,536 Other current liabilities and current maturities of leases and long-term debt $ ( 753 ) Finance lease liabilities ( 11,774 ) Total finance lease liabilities $ ( 12,527 ) Maturities of lease liabilities as of December 31, 2019 are as follows: Operating Leases Finance Leases 2020 $ 1,465 $ 1,597 2021 1,337 1,602 2022 1,178 1,623 2023 708 1,646 2024 — 1,670 2025 and thereafter — 9,799 Total payments $ 4,688 $ 17,937 Less imputed interest ( 427 ) ( 5,410 ) Total $ 4,261 $ 12,527

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
Commitments and Contingencies	Dec. 31, 2019
Commitments and Contingencies [Abstract]
Commitments and Contingencies	12. COMMITMENTS AND CONTINGENCIES Royalty Agreements. The Company has royalty agreements in place with terms that include payment of royalties of 3 % to 5 % of specified product sales. One royalty agreement remains in effect through 2023 , while the other agreement remains in effect the later of 2025 or until expiration of the underlying patents or patent applications. Parties to the royalty agreements have the right at any time to terminate the agreement immediately for cause. Royalty expense of $ 2,892 , $ 2,715 and $ 2,323 was recorded as part of cost of revenue for the years ended December 31, 2019, 2018 and 2017. Purchase Agreements. The Company enters into standard purchase agreements with certain vendors in the ordinary course of business, generally with terms that allow cancellation. 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. The Company acquired nContact Surgical, Inc. pursuant to a merger agreement dated October 4, 2015. The merger agreement provides for contingent consideration or “earnout” to be paid upon attaining specified regulatory approvals and clinical and revenue milestones. The merger agreement’s earnout provisions require the Company to deliver periodic earnout reports to a designated representative of former nContact stockholders. In response to the reports delivered in and after February 2018, the Company received letters from the representative purporting to serve as “earnout objection statements” (as that term is defined in the merger agreement) and claim that for purposes of determining the commercial milestone payment, the Company should be including revenues of certain products that the Company has not included in its earnout statements. The representative is seeking indemnification under the merger agreement related to its claims. The Company has engaged with the representative regarding the earnout objection statements and disputes the basis of the representative’s claims.

Revenue

Revenue	12 Months Ended
Revenue	Dec. 31, 2019
Revenue [Abstract]
Revenue	13. 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 ablation, minimally invasive ablation, 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 $ 1,485 , $ 1,236 and $ 1,090 in 2019, 2018 and 2017. 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 the expected value method considering historical experience. The Company does not provide customers with the right to a refund. In connection with the acquisition of SentreHEART, the Company recognized an allowance for sales returns and refunds of $2,240 for transition to ASC 606 to reflect SentreHEART’s historical refund practices. 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 18 for disaggregated revenue by geographic area and by product category.

Income Taxes

Income Taxes	12 Months Ended
Income Taxes	Dec. 31, 2019
Income Taxes [Abstract]
Income Taxes	14. 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. As of December 31, 2018, the Company completed our accounting for the tax effects of enactment of the Tax Reform Act. 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 did not make this election due to its full valuation allowance. The Company’s provision for income taxes for each of the years ended December 31 is as follows: 2019 2018 2017 Current Tax Expense Federal $ ( 26 ) $ ( 51 ) $ — State 34 28 44 Foreign 165 198 72 Total current tax expense 173 175 116 Deferred Tax Expense Federal $ ( 7,655 ) $ ( 3,048 ) $ 18,485 State ( 1,368 ) 178 ( 1,337 ) Foreign ( 1,690 ) 45 ( 2,241 ) Change in valuation allowance 10,739 2,876 ( 15,009 ) Total deferred tax expense 26 51 ( 102 ) Total tax expense $ 199 $ 226 $ 14 The detail of deferred tax assets and liabilities at December 31 is as follows: 2019 2018 Deferred tax assets (liabilities): Net operating loss carryforward $ 111,000 $ 68,563 Research and development and AMT credit carryforwards, net 8,193 6,206 Deferred interest 909 774 Equity compensation 8,233 4,750 Accruals and reserves 3,513 802 Inventories 1,007 726 Intangible assets ( 30,996 ) ( 11,448 ) Property and equipment, net ( 1,482 ) ( 608 ) Finance and operating lease liabilities 4,016 — Right-of-use assets ( 3,476 ) — Other, net 287 135 Subtotal 101,204 69,900 Less valuation allowance ( 101,178 ) ( 69,849 ) Total $ 26 $ 51 The Company recorded $ 20,590 of net deferred tax assets and offsetting valuation allowances as part of the SentreHEART acquisition. The Company has federal net operating loss carryforwards of $ 340,079 which have expirations between 2021 and 2038 and $ 80,101 which has no expiration as a result of the Tax Reform Act. The Company has state and local net operating loss carryforwards of $ 260,924 with varying expirations from 2020 to 2040 . 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 $ 8,168 which have expirations between 2023 and 2040 . Additionally, the Company has foreign net operating loss carryforwards of approximately $ 42,712 which have expirations between 2020 and 2028 . 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. On January 1, 2019 the Company adopted ASC 842 and recognized $ 400 of operating lease liability deferred tax assets and $ 400 of offsetting right-of-use asset deferred tax liabilities. The Company’s 2019, 2018 and 2017 effective income tax rates differ from the federal statutory rate as follows: 2019 2018 2017 Federal tax at statutory rate 21.00 % $ ( 6,950 ) 21.00 % $ ( 4,391 ) 34.00 % $ ( 9,139 ) Federal and Foreign tax rate change 1.40 ( 462 ) ( 6.84 ) 1,430 ( 109.68 ) 29,480 Federal R&D credit 2.53 ( 837 ) 4.39 ( 918 ) ( 0.40 ) 107 Federal deferred adjustment 3.28 ( 1,085 ) ( 10.77 ) 2,253 — — Federal NOL adjustment for ASU — — — — 10.48 ( 2,816 ) Valuation allowance ( 32.45 ) 10,739 ( 13.75 ) 2,876 55.84 ( 15,009 ) State income taxes 4.02 ( 1,334 ) ( 0.99 ) 206 4.81 ( 1,292 ) Foreign NOL rate change ( 1.17 ) 388 ( 1.22 ) 256 1.30 ( 348 ) Foreign tax rate differential ( 0.38 ) 126 ( 0.60 ) 125 ( 2.45 ) 658 Permanent differences and other 1.17 ( 386 ) 7.70 ( 1,611 ) 6.05 ( 1,627 ) Effective tax rate ( 0.60 ) % $ 199 ( 1.08 ) % $ 226 ( 0.05 ) % $ 14 The Company’s pre-tax book loss for domestic and international operations was $( 28,002 ) and $( 6,993 ) for 2019, $( 13,443 ) and $( 7,468 ) for 2018 and $( 19,409 ) and $( 7,469 ) for 2017. The Company had undistributed earnings of foreign subsidiaries of approximately $ 304 at December 31, 2019. 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 2016 are open for examination. Generally, state and foreign income tax returns for periods beginning in 2015 are open for examination. However, taxing authorities have the ability to adjust net operating loss and tax credit carryforwards from years prior to these periods. The Company has not recognized certain tax benefits because of the uncertainty of realizing the entire value of the tax position taken on income tax returns upon review by the taxing authorities. A reconciliation of the change in federal and state unrecognized tax benefits for 2019, 2018 and 2017 is presented below: 2019 2018 2017 Balance at the beginning of the year $ 1,157 $ 1,157 $ 3,175 Increases (decreases) for prior year tax positions 620 — ( 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 $ 1,777 $ 1,157 $ 1,157 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’s increase for prior year tax positions relates to uncertain income tax benefits assumed pursuant to the SentreHEART acquisition. Historically, the Company did not have any interest and penalties accrued for unrecognized income tax benefits as a result of offsetting net operating losses. The Company has accrued interest and penalties associated with uncertain income tax benefits assumed pursuant to the SentreHEART acquisition as of December 31, 2019, and recognized interest and penalties within income tax expense. The amount is not significant. There are no amounts included in the balance of unrecognized tax benefits at December 31, 2018 and 2017 that, if recognized, would affect the effective tax rate. The balance of unrecognized tax benefits at December 31, 2019 includes $ 1,777 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, 2019.

Concentrations

Concentrations	12 Months Ended
Concentrations	Dec. 31, 2019
Concentrations [Abstract]
Concentrations	15. CONCENTRATIONS During 2019, 2018 and 2017, approximately 12.0 %, 10.8 % and 13.2 % of the Company’s total net revenue was derived from its top ten customers. During 2019, 2018 and 2017 no individual customer accounted for more than 10% of the Company’s revenue. As of December 31, 2019 and 2018, 16.5 % and 11.8 % 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, 2019 and 2018. The Company maintains cash and cash equivalents balances at financial institutions which at times exceed FDIC limits. As of December 31, 2019, $ 28,096 of the cash and cash equivalents balance was in excess of the FDIC limits.

Employee Benefit Plans

Employee Benefit Plans	12 Months Ended
Employee Benefit Plans	Dec. 31, 2019
Employee Benefit Plans [Abstract]
Employee Benefit Plans	16. 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 2019, 2018 and 2017 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 2019, 2018 and 2017 were $ 1,915 , $ 1,560 and $ 1,367 . 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 2019, 2018 or 2017. The Company also provides retirement benefits for employees of AtriCure Europe B.V. and other foreign subsidiaries. Total contributions to retirement plans for these employees were $ 248 , $ 243 and $ 205 in 2019, 2018 and 2017.

Equity Compensation Plans

Equity Compensation Plans	12 Months Ended
Equity Compensation Plans	Dec. 31, 2019
Equity Compensation Plans [Abstract]
Equity Compensation Plans	17. 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 or 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, 2019, 11,999 shares of common stock had been reserved for issuance under the 2014 Plan and 1,578 shares were available for future grants. During 2019 and 2018, the Compensation Committee approved the grant of performance share awards 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 PSAs (PSA Grant Form) provides, among other things, that (i) each PSA that vests represents the right to receive one share of the Company’s common stock; (ii) the PSAs vest based on the Company achieving specified performance measurements over a performance period of three years; (iii) the performance measurements include revenue CAGR as defined in the PSA Grant Form; (iv) threshold, target and maximum payout opportunities established for the 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 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 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 PSA Grant Form). With respect to the 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. The Company estimated the fair value of the 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, restricted stock awards, and restricted stock units granted generally vest at a rate of 33.3 % on the first, second and third anniversaries of the grant date. Stock options granted prior to 2018 under the 2014 Plan 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 year and four years from the date of grant. Stock options generally expire ten years from the date of grant. Activity under the plans during 2019 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, 2019 1,582 $ 13.83 Granted 42 28.77 Exercised ( 110 ) 10.91 Cancelled ( 7 ) 30.48 Outstanding at December 31, 2019 1,507 $ 14.38 4.25 $ 27,340 Vested and expected to vest 1,503 $ 14.35 4.24 $ 27,319 Exercisable at December 31, 2019 1,392 $ 13.55 3.90 $ 26,398 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, 2019 1,746 $ 18.19 90 $ 17.71 Awarded 435 30.12 174 30.77 Released ( 776 ) 18.44 — — Forfeited ( 3 ) 18.02 — — Outstanding at December 31, 2019 1,402 $ 21.76 264 $ 26.34 Weighted Weighted Average Number of Average Remaining Aggregate Shares Exercise Contractual Intrinsic Performance Stock Options Outstanding Price Term Value Outstanding at January 1, 2019 450 $ 13.48 Granted — — Exercised — — Cancelled — — Outstanding at December 31, 2019 450 $ 13.48 3.45 $ 8,566 Exercisable at December 31, 2019 350 $ 13.48 3.45 $ 6,662 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 The total intrinsic value of options exercised during the years ended December 31, 2019, 2018 and 2017 was $ 1,985 , $ 5,343 and $ 5,121 . 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 2019, 2018 and 2017, $ 1,202 , $ 6,012 and $ 4,402 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 2019, 2018 and 2017 was $ 23,479 , $ 11,864 and $ 6,235 . 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. 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 was recognized over the estimated vesting terms. 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, 2019, there were 491 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 for 2019, 2018 and 2017. The expense was allocated as follows: 2019 2018 2017 Cost of revenue $ 917 $ 1,545 $ 610 Research and development expenses 2,374 1,987 2,052 Selling, general and administrative expenses 14,686 12,963 11,953 Total $ 17,977 $ 16,495 $ 14,615 The expense by award type was allocated as follows: 2019 2018 2017 Restricted Stock Awards & Time-Based Stock Options $ 13,922 $ 15,032 $ 13,908 Performance Share Awards 3,254 766 — Performance Stock Options — — 43 ESPP 801 697 664 Total $ 17,977 $ 16,495 $ 14,615 As of December 31, 2019 there was $ 17,971 of unrecognized compensation costs related to non-vested stock options and restricted stock arrangements ($ 997 relating to stock options and $ 16,974 relating to restricted stock). This cost is expected to be recognized over a weighted-average period of 1.8 years for stock options and 1.7 years for restricted stock. As of December 31, 2019 there was $ 6,625 of unrecognized compensation costs related to non-vested performance share awards, and this cost is expected to be recognized over a weighted-average period of 1.6 years. In calculating compensation expense, 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. The fair value of the options is estimated on the grant date using the Black-Scholes model including the following assumptions: 2019 2018 2017 Range of risk-free interest rate 1.43 - 2.64 % 2.31 - 3.01 % 1.75 - 2.12 % Range of expected life of stock options (years) 5.13 to 5.69 5.14 to 5.71 5.21 to 5.76 Range of expected volatility of stock 40.00 - 42.00 % 41.00 - 42.00 % 43.00 - 48.00 % Weighted-average volatility 40.87 % 41.51 % 44.50 % 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. 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 2019, 2018 and 2017 was as follows: 2019 2018 2017 Stock options $ 11.56 $ 10.97 $ 8.60 Restricted stock awards 30.12 18.71 19.38 Performance share awards 30.77 17.71 —

Segment and Geographic Informat

Segment and Geographic Information	12 Months Ended
Segment and Geographic Information	Dec. 31, 2019
Segment and Geographic Information [Abstract]
Segment and Geographic Information	18. 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: 2019 2018 2017 United States $ 185,829 $ 162,146 $ 138,387 Europe 27,929 25,912 21,901 Asia 15,976 12,687 13,616 Other international 1,073 885 812 Total international 44,978 39,484 36,329 Total revenue $ 230,807 $ 201,630 $ 174,716 United States revenue by product type was as follows: 2019 2018 2017 Open ablation $ 80,205 $ 72,250 $ 64,517 Minimally invasive ablation 34,842 35,053 34,421 Appendage management 68,166 52,891 37,281 Total ablation and appendage management 183,213 160,194 136,219 Valve tools 2,616 1,952 2,168 Total United States $ 185,829 $ 162,146 $ 138,387 International revenue by product type was as follows: 2019 2018 2017 Open ablation $ 24,945 $ 21,118 $ 20,718 Minimally invasive ablation 8,349 9,176 8,007 Appendage management 11,476 8,988 7,251 Total ablation and appendage management 44,770 39,282 35,976 Valve tools 208 202 353 Total international $ 44,978 $ 39,484 $ 36,329 The Company’s long-lived assets are located primarily in the United States, except for $ 1,228 as of December 31, 2019 and $ 1,296 as of December 31, 2018, which are located primarily in Europe.

Selected Quarterly Financial Da

Selected Quarterly Financial Data	12 Months Ended
Selected Quarterly Financial Data	Dec. 31, 2019
Selected Quarterly Financial Data [Abstract]
Selected Quarterly Financial Data	19. SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) For the Three Months Ended March 31, June 30, September 30, December 31, 2019 2018 2019 2018 2019 2018 2019 2018 Operating Results: Revenue $ 53,966 $ 46,994 $ 58,906 $ 51,802 $ 56,614 $ 49,941 $ 61,321 $ 52,893 Gross profit 39,871 34,503 43,893 38,079 41,797 35,948 44,774 38,590 Loss from operations ( 5,320 ) ( 9,430 ) ( 3,839 ) 958 ( 8,637 ) ( 6,048 ) ( 15,326 ) ( 2,607 ) Net loss ( 5,635 ) ( 10,134 ) ( 4,101 ) ( 338 ) ( 9,362 ) ( 7,235 ) ( 16,096 ) ( 3,430 ) Net loss per share (basic and diluted) $ ( 0.15 ) $ ( 0.31 ) $ ( 0.11 ) $ ( 0.01 ) $ ( 0.25 ) $ ( 0.22 ) $ ( 0.42 ) $ ( 0.09 ) 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
Schedule II - Valuation And Qualifying Accounts	Dec. 31, 2019
SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]
Schedule of Valuation and Qualifying Accounts Disclosure	SCH EDULE II VALUATION AND QUALIFYING ACCOUNTS Beginning Additions Ending Balance Expenses Other (1) Deductions Balance Reserve for sales returns and allowances Year ended December 31, 2019 $ 1,410 $ 369 $ 2,240 $ 40 $ 3,979 Year ended December 31, 2018 1,169 $ 312 $ — $ 71 $ 1,410 Year ended December 31, 2017 834 $ 441 $ — $ 106 $ 1,169 Allowance for inventory valuation Year ended December 31, 2019 $ 1,029 $ 848 $ — $ 360 $ 1,517 Year ended December 31, 2018 889 $ 718 $ — $ 578 $ 1,029 Year ended December 31, 2017 1,080 $ 1,004 $ — $ 1,195 $ 889 Valuation allowance for deferred tax assets Year ended December 31, 2019 $ 69,849 $ 10,739 $ 20,590 $ — $ 101,178 Year ended December 31, 2018 66,973 $ 2,876 $ — $ — $ 69,849 Year ended December 31, 2017 81,982 $ — $ — $ 15,009 $ 66,973 (1) In connection with the acquisition of SentreHEART, the Company recognized an allowance for sales returns and refunds of for transition to ASC 606 to reflect SentreHEART’s historical refund practices, and recorded an offsetting valuation allowance for deferred tax assets.

Description of Business and S_2

Description of Business and Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2019
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 AtriCure, Inc. and our wholly-owned subsidiaries. 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 purchase as cash equivalents. Cash equivalents include demand deposits, money market funds and repurchase agreements on deposit with certain financial institutions.
Investments	Investments— The Company makes 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 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 13 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 using the expected value method 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, 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 expenses. The Company 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 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. Inventory reserves for excess, obsolete and expired products are impacted by uncertain timing of regulatory approvals, variability in product launch strategies and variation in product use. 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 8). The Company reassesses the useful lives of property and equipment at least 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 at least annually 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 technologies which have 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. The IPR&D assets represent estimates of the fair value of the pre-market approval (PMA) that may result from the CONVERGE IDE and aMAZE IDE clinical trials. The Company reviews intangible assets for impairment using its best estimates based on reasonable and supportable assumptions and projections of expected future cash flows. The Company performs impairment testing annually on October 1. If the IPR&D project is abandoned or regulatory approvals are not obtained, we may have a full or partial impairment charge related to the IPR&D, calculated as the excess carrying value of the IPR&D assets over the estimated fair value.
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 tests goodwill for impairment annually on October 1, or more often if impairment indicators are present.
Other Noncurrent Liabilities	Contingent Consideration and other Noncurrent Liabilities— This balance consists of the contingent consideration recorded in business combinations, as well as deferred revenues, asset retirement obligations and other contractual obligations. The 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 and SentreHEART 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 transacted 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 significant estimates and judgments about 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 the deferred income tax asset will not be realized. Significant weight is given to evidence that can be objectively verified. The Company evaluates deferred income tax assets on an annual basis to determine if valuation allowances are required. 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, and tax planning strategies that are both prudent and feasible. In evaluating the need for a valuation allowance, 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. The Tax Cut and Jobs Act (Tax Reform Act) allows companies an election to reclassify the income tax effects of the Tax Reform Act on items within accumulated other comprehensive income (loss) to retained earnings. The Company has not made this election due to its full valuation allowance.
Net Loss Per Share	Net Loss Per Share— Basic and diluted net loss per share is computed 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 3,623 , 3,869 and 4,321 stock options, restricted stock awards, restricted stock units and performance share awards as of December 31, 2019, 2018 and 2017 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): 2019 2018 2017 Total accumulated other comprehensive (loss) income at beginning of period $ ( 199 ) $ 34 $ ( 468 ) Unrealized gains (losses) on investments Balance at beginning of period $ ( 37 ) $ ( 6 ) $ ( 21 ) Other comprehensive income (loss) before reclassifications 137 ( 31 ) 15 Amounts reclassified from accumulated other comprehensive (loss) income to other income — — — Balance at end of period $ 100 $ ( 37 ) $ ( 6 ) Foreign currency translation adjustment Balance at beginning of period $ ( 162 ) $ 40 $ ( 447 ) Other comprehensive (loss) income before reclassifications ( 277 ) ( 367 ) 660 Amounts reclassified from accumulated other comprehensive (loss) income to other income 181 165 ( 173 ) Balance at end of period $ ( 258 ) $ ( 162 ) $ 40 Total accumulated other comprehensive (loss) income at end of period $ ( 158 ) $ ( 199 ) $ 34
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 $ 635 , $ 785 and $ 900 during the years ended December 31, 2019, 2018 and 2017.
Share-Based Compensation	Share-Based Compensation— The Company records 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. The Company estimates the fair value of share-based payment awards on the date of grant. 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 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 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 estimated fair value of performance share awards may be adjusted over the performance period based on changes to estimates of performance target achievement. 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, repurchase agreements, 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 measurements of the Level 3 contingent consideration liabilities 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, 2019
Description of Business and Summary of Significant Accounting Policies [Abstract]
Accumulated Other Comprehensive Income (Loss)	2019 2018 2017 Total accumulated other comprehensive (loss) income at beginning of period $ ( 199 ) $ 34 $ ( 468 ) Unrealized gains (losses) on investments Balance at beginning of period $ ( 37 ) $ ( 6 ) $ ( 21 ) Other comprehensive income (loss) before reclassifications 137 ( 31 ) 15 Amounts reclassified from accumulated other comprehensive (loss) income to other income — — — Balance at end of period $ 100 $ ( 37 ) $ ( 6 ) Foreign currency translation adjustment Balance at beginning of period $ ( 162 ) $ 40 $ ( 447 ) Other comprehensive (loss) income before reclassifications ( 277 ) ( 367 ) 660 Amounts reclassified from accumulated other comprehensive (loss) income to other income 181 165 ( 173 ) Balance at end of period $ ( 258 ) $ ( 162 ) $ 40 Total accumulated other comprehensive (loss) income at end of period $ ( 158 ) $ ( 199 ) $ 34

Fair Value (Tables)

Fair Value (Tables)	12 Months Ended
Fair Value (Tables)	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
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, 2019: 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 $ — $ 14,502 $ — $ 14,502 Repurchase agreements — 10,000 — 10,000 Commercial paper — 13,755 — 13,755 U.S. government agencies and securities 8,539 — — 8,539 Corporate bonds — 24,852 — 24,852 Asset-backed securities — 18,847 — 18,847 Total assets $ 8,539 $ 81,956 $ — $ 90,495 Liabilities: Acquisition-related contingent consideration $ — $ — $ 185,157 $ 185,157 Total liabilities $ — $ — $ 185,157 $ 185,157 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
Level 3 Fair Value Measurements Using Significant Other Unobservable Inputs for Acquisition-Related Contingent Consideration	2019 2018 2017 Beginning Balance – January 1 $ 18,773 $ 37,098 $ 41,176 Amounts acquired 171,300 — — Settlement of trial enrollment milestone — ( 7,500 ) — Changes in fair value included in selling, general and administrative expenses ( 4,916 ) ( 10,825 ) ( 4,078 ) Ending Balance – December 31 $ 185,157 $ 18,773 $ 37,098
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Level 3 Fair Value Measurements Using Significant Other Unobservable Inputs for Acquisition-Related Contingent Consideration	Weighted average Fair Value Valuation Technique Input Range by relative fair value Discount rate 5.56 % 5.56 % Regulatory & Commercialization-based milestones $ 185,157 Probability-weighted scenario approach Projected month and year of payment June 2020 - September 2025 n/a Probability of payment 77.40 - 85.00 % 81.75 %

Investments (Tables)

Investments (Tables)	12 Months Ended
Investments (Tables)	Dec. 31, 2019
Investments [Abstract]
Summary of Short-term Investments	Investments as of December 31, 2019 consisted of the following: Unrealized Gains Cost Basis (Losses) Fair Value Corporate bonds $ 24,796 $ 56 $ 24,852 U.S. government agencies and securities 8,529 10 8,539 Commercial paper 13,755 — 13,755 Asset-backed securities 18,813 34 18,847 Total $ 65,893 $ 100 $ 65,993 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

Business Combinations (Tables)

Business Combinations (Tables)	12 Months Ended
Business Combinations (Tables)	Dec. 31, 2019
Business Combinations [Abstract]
Schedule of Components of Aggregate Purchase Price	Fair value of AtriCure common stock issued at closing $ 20,307 Cash 17,240 Fair value of contingent consideration liabilities 171,300 Total purchase price $ 208,847
Summary of Estimated Fair Values of Assets Acquired and Liabilities Assumed	August 13, 2019 Inventories $ 1,848 Current assets 328 Operating lease right-of-use asset 2,929 Property and equipment 94 Intangible assets 82,570 Other assets 202 Total identifiable assets $ 87,971 Current liabilities $ 5,719 Operating lease liability 2,929 Total liabilities assumed $ 8,648 Net identifiable assets acquired $ 79,323 Goodwill 129,524 Total consideration $ 208,847
Valuation of Intangible Assets Acquired and Related Amortization Periods	Amortization Term Valuation (in years) Developed technology $ 270 15 IPR&D 82,300 Indefinite Total $ 82,570
Pro-forma Acquisition Information	Year Ended December 31, (unaudited) 2019 2018 Revenue $ 232,768 $ 205,725 Net loss ( 40,970 ) ( 42,959 ) Basic and diluted net loss per share $ ( 1.09 ) $ ( 1.23 )

Intangible Assets And Goodwill

Intangible Assets And Goodwill (Tables)	12 Months Ended
Intangible Assets And Goodwill (Tables)	Dec. 31, 2019
Intangible Assets And Goodwill [Abstract]
Company's Intangible Assets	2019 2018 Estimated Accumulated Accumulated Useful Life Cost Amortization Cost Amortization Technology 3 - 15 years $ 11,691 $ 8,131 $ 12,250 $ 7,017 IPR&D 126,321 — 44,021 — Total $ 138,012 $ 8,131 $ 56,271 $ 7,017
Future Amortization Expense Related to Intangible Assets with Definite Lives	2020 $ 1,822 2021 1,511 2022 18 2023 18 2024 18 2025 and thereafter 173 Total $ 3,560
Summary of Company's Goodwill	Net carrying amount as of December 31, 2017 $ 105,257 Additions — Net carrying amount as of December 31, 2018 105,257 Additions 129,524 Net carrying amount as of December 31, 2019 $ 234,781

Inventories (Tables)

Inventories (Tables)	12 Months Ended
Inventories (Tables)	Dec. 31, 2019
Inventories [Abstract]
Summary Of Inventories	2019 2018 Raw materials $ 11,126 $ 9,100 Work in process 1,260 1,232 Finished goods 17,028 12,152 Inventories $ 29,414 $ 22,484

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
Property and Equipment (Tables)	Dec. 31, 2019
Property and Equipment [Abstract]
Summary of Property and Equipment	Estimated Useful Life 2019 2018 Generators and other capital equipment 1 - 3 years $ 20,167 $ 18,158 Building under finance lease 15 years 14,250 14,250 Computer and other office equipment 3 years 7,606 6,360 Machinery, equipment and vehicles 3 - 7 years 5,905 4,859 Furniture and fixtures 3 - 7 years 5,009 4,702 Leasehold improvements 5 - 15 years 6,078 3,943 Construction in progress N/A 5,708 1,868 Land N/A 502 — Equipment under finance leases 3 - 5 years 483 213 Total 65,708 54,353 Less accumulated depreciation ( 33,062 ) ( 27,273 ) Property and equipment, net $ 32,646 $ 27,080

Accrued Liabilities (Tables)

Accrued Liabilities (Tables)	12 Months Ended
Accrued Liabilities (Tables)	Dec. 31, 2019
Accrued Liabilities [Abstract]
Accrued Liabilities	2019 2018 Accrued bonus $ 10,840 $ 9,100 Accrued commissions 8,734 8,065 Accrued payroll and employee-related expenses 6,748 4,512 Sales returns and allowances 3,979 1,410 Other accrued liabilities 59 1,205 Accrued taxes and value-added taxes payable 1,658 886 Accrued royalties 732 662 Total $ 32,750 $ 25,840

Indebtedness (Tables)

Indebtedness (Tables)	12 Months Ended
Indebtedness (Tables)	Dec. 31, 2019
Indebtedness [Abstract]
Future Maturities On Debt	2020 $ — 2021 14,634 2022 17,561 2023 17,561 2024 10,244 Total long-term debt, of which $ 60,000 is noncurrent $ 60,000

Leases (Tables)

Leases (Tables)	12 Months Ended
Leases (Tables)	Dec. 31, 2019
Leases [Abstract]
Summary Of Components Of Lease Expense	Twelve Months Ended December 31, 2019 Operating lease cost $ 952 Finance lease cost: Amortization of right-of-use assets 998 Interest on lease liabilities 872 Total finance lease cost $ 1,870
Summary Of Supplemental Cash Flow Information Related To Leases	Twelve Months Ended December 31, 2019 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from operating leases $ 1,026 Operating cash flows from finance leases 872 Financing cash flows from finance leases 629 Right-of-use assets obtained in exchange for lease obligations: Operating Leases 1,884 Finance Leases 270 Operating lease right-of-use asset obtained in business combination 2,929
Summary Of Supplemental Balance Sheet Information Related To Leases	December 31, 2019 Operating Leases Operating lease right-of-use assets $ 4,032 Other current liabilities and current maturities of leases and long-term debt ( 1,465 ) Operating lease liabilities ( 2,796 ) Total operating lease liabilities $ ( 4,261 ) Finance Leases Property and equipment, at cost $ 14,733 Accumulated depreciation ( 4,197 ) Property and equipment, net $ 10,536 Other current liabilities and current maturities of leases and long-term debt $ ( 753 ) Finance lease liabilities ( 11,774 ) Total finance lease liabilities $ ( 12,527 )
Schedule Of Maturities Of Lease Liabilities	Operating Leases Finance Leases 2020 $ 1,465 $ 1,597 2021 1,337 1,602 2022 1,178 1,623 2023 708 1,646 2024 — 1,670 2025 and thereafter — 9,799 Total payments $ 4,688 $ 17,937 Less imputed interest ( 427 ) ( 5,410 ) Total $ 4,261 $ 12,527

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
Income Taxes (Tables)	Dec. 31, 2019
Income Taxes [Abstract]
Summary Of Company's Provision for Income Taxes	2019 2018 2017 Current Tax Expense Federal $ ( 26 ) $ ( 51 ) $ — State 34 28 44 Foreign 165 198 72 Total current tax expense 173 175 116 Deferred Tax Expense Federal $ ( 7,655 ) $ ( 3,048 ) $ 18,485 State ( 1,368 ) 178 ( 1,337 ) Foreign ( 1,690 ) 45 ( 2,241 ) Change in valuation allowance 10,739 2,876 ( 15,009 ) Total deferred tax expense 26 51 ( 102 ) Total tax expense $ 199 $ 226 $ 14
Summary of Detail of Deferred Tax Assets and Liabilities	2019 2018 Deferred tax assets (liabilities): Net operating loss carryforward $ 111,000 $ 68,563 Research and development and AMT credit carryforwards, net 8,193 6,206 Deferred interest 909 774 Equity compensation 8,233 4,750 Accruals and reserves 3,513 802 Inventories 1,007 726 Intangible assets ( 30,996 ) ( 11,448 ) Property and equipment, net ( 1,482 ) ( 608 ) Finance and operating lease liabilities 4,016 — Right-of-use assets ( 3,476 ) — Other, net 287 135 Subtotal 101,204 69,900 Less valuation allowance ( 101,178 ) ( 69,849 ) Total $ 26 $ 51
Summary Of Difference Between Effective Income Tax Rates and Federal Statutory Rate	2019 2018 2017 Federal tax at statutory rate 21.00 % $ ( 6,950 ) 21.00 % $ ( 4,391 ) 34.00 % $ ( 9,139 ) Federal and Foreign tax rate change 1.40 ( 462 ) ( 6.84 ) 1,430 ( 109.68 ) 29,480 Federal R&D credit 2.53 ( 837 ) 4.39 ( 918 ) ( 0.40 ) 107 Federal deferred adjustment 3.28 ( 1,085 ) ( 10.77 ) 2,253 — — Federal NOL adjustment for ASU — — — — 10.48 ( 2,816 ) Valuation allowance ( 32.45 ) 10,739 ( 13.75 ) 2,876 55.84 ( 15,009 ) State income taxes 4.02 ( 1,334 ) ( 0.99 ) 206 4.81 ( 1,292 ) Foreign NOL rate change ( 1.17 ) 388 ( 1.22 ) 256 1.30 ( 348 ) Foreign tax rate differential ( 0.38 ) 126 ( 0.60 ) 125 ( 2.45 ) 658 Permanent differences and other 1.17 ( 386 ) 7.70 ( 1,611 ) 6.05 ( 1,627 ) Effective tax rate ( 0.60 ) % $ 199 ( 1.08 ) % $ 226 ( 0.05 ) % $ 14
Summary Of Reconciliation of Change in Federal and State Unrecognized Tax Benefits	2019 2018 2017 Balance at the beginning of the year $ 1,157 $ 1,157 $ 3,175 Increases (decreases) for prior year tax positions 620 — ( 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 $ 1,777 $ 1,157 $ 1,157

Equity Compensation Plans (Tabl

Equity Compensation Plans (Tables)	12 Months Ended
Equity Compensation Plans (Tables)	Dec. 31, 2019
Equity Compensation Plans [Abstract]
Activity Under Stock Based Compensation Plans	Activity under the plans during 2019 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, 2019 1,582 $ 13.83 Granted 42 28.77 Exercised ( 110 ) 10.91 Cancelled ( 7 ) 30.48 Outstanding at December 31, 2019 1,507 $ 14.38 4.25 $ 27,340 Vested and expected to vest 1,503 $ 14.35 4.24 $ 27,319 Exercisable at December 31, 2019 1,392 $ 13.55 3.90 $ 26,398 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, 2019 1,746 $ 18.19 90 $ 17.71 Awarded 435 30.12 174 30.77 Released ( 776 ) 18.44 — — Forfeited ( 3 ) 18.02 — — Outstanding at December 31, 2019 1,402 $ 21.76 264 $ 26.34 Weighted Weighted Average Number of Average Remaining Aggregate Shares Exercise Contractual Intrinsic Performance Stock Options Outstanding Price Term Value Outstanding at January 1, 2019 450 $ 13.48 Granted — — Exercised — — Cancelled — — Outstanding at December 31, 2019 450 $ 13.48 3.45 $ 8,566 Exercisable at December 31, 2019 350 $ 13.48 3.45 $ 6,662 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
Share-Based Compensation Expense Related to Employee Share-Based Compensation	2019 2018 2017 Cost of revenue $ 917 $ 1,545 $ 610 Research and development expenses 2,374 1,987 2,052 Selling, general and administrative expenses 14,686 12,963 11,953 Total $ 17,977 $ 16,495 $ 14,615 The expense by award type was allocated as follows: 2019 2018 2017 Restricted Stock Awards & Time-Based Stock Options $ 13,922 $ 15,032 $ 13,908 Performance Share Awards 3,254 766 — Performance Stock Options — — 43 ESPP 801 697 664 Total $ 17,977 $ 16,495 $ 14,615
Assumptions Used for Determining Fair Value of Options	2019 2018 2017 Range of risk-free interest rate 1.43 - 2.64 % 2.31 - 3.01 % 1.75 - 2.12 % Range of expected life of stock options (years) 5.13 to 5.69 5.14 to 5.71 5.21 to 5.76 Range of expected volatility of stock 40.00 - 42.00 % 41.00 - 42.00 % 43.00 - 48.00 % Weighted-average volatility 40.87 % 41.51 % 44.50 % 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	2019 2018 2017 Stock options $ 11.56 $ 10.97 $ 8.60 Restricted stock awards 30.12 18.71 19.38 Performance share awards 30.77 17.71 —

Segment and Geographic Inform_2

Segment and Geographic Information (Tables)	12 Months Ended
Segment and Geographic Information (Tables)	Dec. 31, 2019
Segment and Geographic Information [Abstract]
Revenue by Geographic Area	2019 2018 2017 United States $ 185,829 $ 162,146 $ 138,387 Europe 27,929 25,912 21,901 Asia 15,976 12,687 13,616 Other international 1,073 885 812 Total international 44,978 39,484 36,329 Total revenue $ 230,807 $ 201,630 $ 174,716
Revenue by Product Type	United States revenue by product type was as follows: 2019 2018 2017 Open ablation $ 80,205 $ 72,250 $ 64,517 Minimally invasive ablation 34,842 35,053 34,421 Appendage management 68,166 52,891 37,281 Total ablation and appendage management 183,213 160,194 136,219 Valve tools 2,616 1,952 2,168 Total United States $ 185,829 $ 162,146 $ 138,387 International revenue by product type was as follows: 2019 2018 2017 Open ablation $ 24,945 $ 21,118 $ 20,718 Minimally invasive ablation 8,349 9,176 8,007 Appendage management 11,476 8,988 7,251 Total ablation and appendage management 44,770 39,282 35,976 Valve tools 208 202 353 Total international $ 44,978 $ 39,484 $ 36,329

Selected Quarterly Financial _2

Selected Quarterly Financial Data (Tables)	12 Months Ended
Selected Quarterly Financial Data (Tables)	Dec. 31, 2019
Selected Quarterly Financial Data [Abstract]
Schedule of Quarterly Financial Information	For the Three Months Ended March 31, June 30, September 30, December 31, 2019 2018 2019 2018 2019 2018 2019 2018 Operating Results: Revenue $ 53,966 $ 46,994 $ 58,906 $ 51,802 $ 56,614 $ 49,941 $ 61,321 $ 52,893 Gross profit 39,871 34,503 43,893 38,079 41,797 35,948 44,774 38,590 Loss from operations ( 5,320 ) ( 9,430 ) ( 3,839 ) 958 ( 8,637 ) ( 6,048 ) ( 15,326 ) ( 2,607 ) Net loss ( 5,635 ) ( 10,134 ) ( 4,101 ) ( 338 ) ( 9,362 ) ( 7,235 ) ( 16,096 ) ( 3,430 ) Net loss per share (basic and diluted) $ ( 0.15 ) $ ( 0.31 ) $ ( 0.11 ) $ ( 0.01 ) $ ( 0.25 ) $ ( 0.22 ) $ ( 0.42 ) $ ( 0.09 )

Description of Business and S_4

Description of Business and Summary of Significant Accounting Policies (Narrative) (Details) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Description Of Business And Significant Accounting Policies [Line Items]
Options, restricted stock and performance based shares excluded from calculation of net loss per share	3,623	3,869	4,321
Advertising costs	$ 635	$ 785	$ 900
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, 2019	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total accumulated other comprehensive (loss) income at beginning of period	$ (199)	$ 34	$ (468)
Total accumulated other comprehensive (loss) income at end of period	(158)	(199)	34
Unrealized Gains on Investments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total accumulated other comprehensive (loss) income at beginning of period	(37)	(6)	(21)
Other comprehensive income (loss) before reclassifications	137	(31)	15
Amounts reclassified from accumulated other comprehensive (loss) income to other income (expense)
Total accumulated other comprehensive (loss) income at end of period	100	(37)	(6)
Foreign Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total accumulated other comprehensive (loss) income at beginning of period	(162)	40	(447)
Other comprehensive income (loss) before reclassifications	(277)	(367)	660
Amounts reclassified from accumulated other comprehensive (loss) income to other income (expense)	181	165	(173)
Total accumulated other comprehensive (loss) income at end of period	$ (258)	$ (162)	$ 40

Fair Value (Narrative) (Details

Fair Value (Narrative) (Details) shares in Thousands	Aug. 13, 2019USD ($)shares	Oct. 13, 2015shares	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2019USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Change in value of contingent consideration			$ (4,916,000)	$ (10,825,000)	$ (4,078,000)
Contingent consideration revenue to target ratio						1.5
Payment of contingent consideration when commercial milestone achieved time allotment period						65 days
Payments of contingent consideration			0	0	0
nContact Surgical [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of AtriCure common stock issued at closing			5,660,000
Shares issued and delivered \| shares		3,757
SentreHEART [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of AtriCure common stock issued at closing	$ 20,307,000		20,307,000
Shares issued and delivered \| shares	699
Preliminary fair value of contingent consideration	$ 171,300,000
Maximum amount of shares that may be issued after closing \| shares	7,021
Shares issued at closing \| shares	699
Maximum contingent consideration payable	$ 260,000,000,000
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				$ (7,500,000)
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			$ 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, 2019	Dec. 31, 2018
Assets:
Total assets	$ 90,495	$ 108,364
Liabilities:
Acquisition-related contingent consideration	185,157	18,773
Total liabilities	185,157	18,773
Money Market Funds [Member]
Assets:
Total assets	14,502	16,193
Repurchase Agreements [Member]
Assets:
Total assets	10,000
Commercial Paper [Member]
Assets:
Total assets	13,755	40,731
U.S. Government Agencies and Securities [Member]
Assets:
Total assets	8,539	6,734
Corporate Bonds [Member]
Assets:
Total assets	24,852	30,195
Asset-backed Securities [Member]
Assets:
Total assets	18,847	14,511
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets:
Total assets	8,539	6,734
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| U.S. Government Agencies and Securities [Member]
Assets:
Total assets	8,539	6,734
Significant Other Observable Inputs (Level 2) [Member]
Assets:
Total assets	81,956	101,630
Significant Other Observable Inputs (Level 2) [Member] \| Money Market Funds [Member]
Assets:
Total assets	14,502	16,193
Significant Other Observable Inputs (Level 2) [Member] \| Repurchase Agreements [Member]
Assets:
Total assets	10,000
Significant Other Observable Inputs (Level 2) [Member] \| Commercial Paper [Member]
Assets:
Total assets	13,755	40,731
Significant Other Observable Inputs (Level 2) [Member] \| Corporate Bonds [Member]
Assets:
Total assets	24,852	30,195
Significant Other Observable Inputs (Level 2) [Member] \| Asset-backed Securities [Member]
Assets:
Total assets	18,847	14,511
Significant Other Unobservable Inputs (Level 3) [Member]
Liabilities:
Acquisition-related contingent consideration	185,157	18,773
Total liabilities	$ 185,157	$ 18,773

Fair Value (Level 3 Fair Value

Fair Value (Level 3 Fair Value Measurements Using Significant Other Unobservable Inputs for Acquisition-Related Contingent Consideration (Recurring)) (Details) - Significant Other Unobservable Inputs (Level 3) [Member] - Fair Value, Measurements, Recurring [Member] $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Regulatory & Commercialization-based milestones	$ 185,157
Minimum [Member] \| Measurement Input, Discount Rate [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Contingent consideration, measurement input	5.56%
Minimum [Member] \| Measurement Input, Probabilty Of Payment [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Contingent consideration, measurement input	77.40%
Maximum [Member] \| Measurement Input, Probabilty Of Payment [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Contingent consideration, measurement input	85.00%
Weighted Average [Member] \| Measurement Input, Discount Rate [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Contingent consideration, measurement input	5.56%
Weighted Average [Member] \| Measurement Input, Probabilty Of Payment [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Contingent consideration, measurement input	81.75%

Fair Value (Level 3 Fair Valu_2

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, 2019	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 18,773	$ 37,098	$ 41,176
Amounts acquired	171,300
Settlement of trial enrollment milestone		(7,500)
Changes in fair value included in selling, general and administrative expenses	(4,916)	(10,825)	(4,078)
Ending Balance	$ 185,157	$ 18,773	$ 37,098

Investments (Narrative) (Detail

Investments (Narrative) (Details) - USD ($)	12 Months Ended
Investments (Narrative) (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Investments [Abstract]
Gain (Loss) on Investments	$ 0	$ 0	$ 0

Investments (Summary Of Short-t

Investments (Summary Of Short-term Investments) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Investment [Line Items]
Short-term investments, Cost Basis	$ 65,893	$ 92,208
Short-term investment, Unrealized Gains (Losses)	100	(37)
Short-term investments, Fair Value	65,993	92,171
Corporate Bonds [Member]
Investment [Line Items]
Short-term investments, Cost Basis	24,796	30,223
Short-term investment, Unrealized Gains (Losses)	56	(28)
Short-term investments, Fair Value	24,852	30,195
U.S. Government Agencies and Securities [Member]
Investment [Line Items]
Short-term investments, Cost Basis	8,529	6,734
Short-term investment, Unrealized Gains (Losses)	10
Short-term investments, Fair Value	8,539	6,734
Commercial Paper [Member]
Investment [Line Items]
Short-term investments, Cost Basis	13,755	40,731
Short-term investments, Fair Value	13,755	40,731
Asset-backed Securities [Member]
Investment [Line Items]
Short-term investments, Cost Basis	18,813	14,520
Short-term investment, Unrealized Gains (Losses)	34	(9)
Short-term investments, Fair Value	$ 18,847	$ 14,511

Business Combinations (Narrativ

Business Combinations (Narrative) (Details) - USD ($) shares in Thousands	Aug. 13, 2019	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Business Combination Transactions [Line Items]
Cash payments to former shareholders										$ 17,240,000
Revenue		$ 61,321,000	$ 56,614,000	$ 58,906,000	$ 53,966,000	$ 52,893,000	$ 49,941,000	$ 51,802,000	$ 46,994,000	230,807,000	$ 201,630,000	$ 174,716,000
Net loss		(16,096,000)	$ (9,362,000)	$ (4,101,000)	$ (5,635,000)	$ (3,430,000)	$ (7,235,000)	$ (338,000)	$ (10,134,000)	(35,194,000)	(21,137,000)	(26,892,000)
Common Stock [Member]
Business Combination Transactions [Line Items]
Net loss
Completion Of CONVERGE IDE Trial And Receiving A PMA From FDA [Member] \| Maximum [Member]
Business Combination Transactions [Line Items]
Contingent liability consideration		42,500,000								42,500,000
SentreHEART [Member]
Business Combination Transactions [Line Items]
Acquisition of shares and voting interest	100.00%
Consideration payment, value	$ 20,307,000									20,307,000
Cash payments to former shareholders	$ 18,008,000
Consideration payment, shares	699
Adjustment for net working capital balances outside of specified range	$ 768,000
Maximum amount of shares that may be issued after closing	7,021
Shares issued at closing	699
Maximum contingent consideration payable	$ 260,000,000,000
Revenue		1,280,000
Net loss		8,505,000
Acquisition related costs										3,978,000
Net deferred tax assets		20,590,000								20,590,000
Federal and state net operating loss carryforwards		184,036,000								184,036,000
Federal net operating loss carryforwards		$ 37,906,000								$ 37,906,000
Business acquisition, net operating loss carryforwards, expiration date										2026
SentreHEART [Member] \| PMA Milestone [Member]
Business Combination Transactions [Line Items]
Milestone payment										$ 25,000,000
Milestone consideration due date										Dec. 31, 2022
Potential contingent consideration reduction percentage, monthly										4.17%
Date of contingent consideration is reduced to zero										Dec. 31, 2023
SentreHEART [Member] \| PMA Milestone [Member] \| Maximum [Member]
Business Combination Transactions [Line Items]
Consideration related to earnout calculation										$ 140,000,000
SentreHEART [Member] \| PMA Milestone After December 31, 2023 [Member]
Business Combination Transactions [Line Items]
Consideration related to earnout calculation										$ 0
SentreHEART [Member] \| CPT Reimbursement Milestone [Member]
Business Combination Transactions [Line Items]
Milestone consideration due date										Dec. 31, 2025
Potential contingent consideration reduction percentage, monthly										4.17%
Date of contingent consideration is reduced to zero										Dec. 31, 2026
SentreHEART [Member] \| CPT Reimbursement Milestone [Member] \| Maximum [Member]
Business Combination Transactions [Line Items]
Milestone payment										$ 120,000,000
SentreHEART [Member] \| CPT Reimbursement Milestone After December 31, 2025 [Member]
Business Combination Transactions [Line Items]
Milestone payment										$ 0

Business Combinations (Schedule

Business Combinations (Schedule of Components of Aggregate Purchase Price) (Details) - SentreHEART [Member] - USD ($) $ in Thousands	Aug. 13, 2019	Dec. 31, 2019
Business Acquisition [Line Items]
Fair value of AtriCure common stock issued at closing	$ 20,307	$ 20,307
Cash		17,240
Fair value of contingent consideration liabilities		171,300
Total purchase price		$ 208,847

Business Combinations (Summary

Business Combinations (Summary Of Estimated Fair Values Of Assets Acquired And Liabilities Assumed) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Aug. 13, 2019	Dec. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Operating lease right-of-use asset	$ 2,929
Goodwill	234,781		$ 105,257	$ 105,257
SentreHEART [Member]
Business Acquisition [Line Items]
Inventories		$ 1,848
Current assets		328
Operating lease right-of-use asset		2,929
Property and equipment		94
Intangible assets	$ 82,570	82,570
Other assets		202
Total identifiable assets		87,971
Current liabilities		5,719
Operating lease liability		2,929
Total liabilities assumed		8,648
Net identifiable assets acquired		79,323
Goodwill		129,524
Total consideration		$ 208,847

Business Combinations (Valuatio

Business Combinations (Valuation of Intangible Assets Acquired and Related Amortization Periods) (Details) - SentreHEART [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Aug. 13, 2019
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible assets	$ 82,570	$ 82,570
Developed Technology [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible assets	$ 270
Intangible assets amortization period	15 years
IPR&D [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible assets	$ 82,300

Business Combination (Pro-forma

Business Combination (Pro-forma Acquisition Information) (Details) - SentreHEART [Member] - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Business Acquisition Pro Forma Information [Line Items]
Revenue	$ 232,768	$ 205,725
Net loss	$ (40,970)	$ (42,959)
Basic and diluted net loss per share	$ (1.09)	$ (1.23)

Intangible Assets And Goodwil_2

Intangible Assets And Goodwill (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	$ 1,943	$ 1,510	$ 1,367
Fusion Technology [Member]
Finite-Lived Intangible Assets [Line Items]
Estimated Useful Life		10 years
Reduction in useful life		2 years
Minimum [Member] \| Fusion Technology [Member]
Finite-Lived Intangible Assets [Line Items]
Estimated Useful Life	3 years
Maximum [Member] \| Fusion Technology [Member]
Finite-Lived Intangible Assets [Line Items]
Estimated Useful Life	15 years

Intangible Assets And Goodwil_3

Intangible Assets And Goodwill (Company's Intangible Assets) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Cost	$ 138,012	$ 56,271
Accumulated Amortization	8,131	$ 7,017
Fusion Technology [Member]
Finite-Lived Intangible Assets [Line Items]
Estimated Useful Life		10 years
Cost	11,691	$ 12,250
Accumulated Amortization	8,131	7,017
IPR&D [Member]
Finite-Lived Intangible Assets [Line Items]
Cost	$ 126,321	$ 44,021
Minimum [Member] \| Fusion Technology [Member]
Finite-Lived Intangible Assets [Line Items]
Estimated Useful Life	3 years
Maximum [Member] \| Fusion Technology [Member]
Finite-Lived Intangible Assets [Line Items]
Estimated Useful Life	15 years

Intangible Assets And Goodwil_4

Intangible Assets And Goodwill (Future Amortization Expense Related to Intangible Assets with Definite Lives) (Details) $ in Thousands	Dec. 31, 2019USD ($)
Intangible Assets And Goodwill [Abstract]
2020	$ 1,822
2021	1,511
2022	18
2023	18
2024	18
2025 and thereafter	173
Total	$ 3,560

Intangible Assets and Goodwil_5

Intangible Assets and Goodwill (Summary Of Company's Goodwill) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Intangible Assets And Goodwill [Abstract]
Goodwill, Beginning Balance	$ 105,257	$ 105,257
Additions	129,524
Goodwill, Ending Balance	$ 234,781	$ 105,257

Inventories (Summary Of Invento

Inventories (Summary Of Inventories) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Inventories [Abstract]
Raw materials	$ 11,126	$ 9,100
Work in process	1,260	1,232
Finished goods	17,028	12,152
Inventories	$ 29,414	$ 22,484

Property and Equipment (Narrati

Property and Equipment (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Depreciation	$ 7,423	$ 7,244	$ 7,761
Net carrying value	32,646	27,080
Generators and Other Capital Equipment [Member]
Property, Plant and Equipment [Line Items]
Depreciation	2,910	3,191	$ 3,574
Net carrying value	$ 4,272	$ 4,545

Property and Equipment (Summary

Property and Equipment (Summary Of Property And Equipment) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 65,708	$ 54,353
Less accumulated depreciation	(33,062)	(27,273)
Property, and equipment, net	32,646	27,080
Generators and Other Capital Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	20,167	18,158
Property, and equipment, net	$ 4,272	4,545
Building [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	15 years
Property and equipment, gross	$ 14,250	14,250
Computer and Other Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	3 years
Property and equipment, gross	$ 7,606	6,360
Machinery, Equipment and Vehicles [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	5,905	4,859
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	5,009	4,702
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	6,078	3,943
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	5,708	1,868
Land [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	502
Equipment Under Finance Leases [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 483	$ 213
Minimum [Member] \| Generators and Other Capital Equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	1 year
Minimum [Member] \| Machinery, Equipment and Vehicles [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	3 years
Minimum [Member] \| Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	3 years
Minimum [Member] \| Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	5 years
Minimum [Member] \| Equipment Under Finance Leases [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	3 years
Maximum [Member] \| Generators and Other Capital Equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	3 years
Maximum [Member] \| Machinery, Equipment and Vehicles [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	7 years
Maximum [Member] \| Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	7 years
Maximum [Member] \| Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	15 years
Maximum [Member] \| Equipment Under Finance Leases [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	5 years

Accrued Liabilities (Accrued Li

Accrued Liabilities (Accrued Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Accrued Liabilities [Abstract]
Accrued bonus	$ 10,840	$ 9,100
Accrued commissions	8,734	8,065
Accrued payroll and employee-related expenses	6,748	4,512
Sales returns and allowances	3,979	1,410
Other accrued liabilities	59	1,205
Accrued taxes and value-added taxes payable	1,658	886
Accrued royalties	732	662
Total	$ 32,750	$ 25,840

Indebtedness (Narrative) (Detai

Indebtedness (Narrative) (Details) - USD ($)	Feb. 23, 2018	Dec. 31, 2019
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]
Line of credit, maximum borrowing capacity		$ 70,000,000
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, borrowings		$ 20,000,000
Maturity date		Aug. 1, 2024
Line of credit, amount outstanding		$ 0
Line of credit, revolving line of credit		$ 8,750,000
Annual commitment fee, percentage		0.15%
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		5.00%
Term Loan [Member] \| Silicon Valley Bank, Amended And Restated Loan Agreement Effective 2/23/18 [Member]
Line of Credit Facility [Line Items]
Loan amount	$ 60,000,000
Term loan principal payment start date		Mar. 1, 2021
Annual commitment fee		$ 135,000
Annual commitment fee, percentage		3.00%
Financing costs		$ 501,000
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		0.75%
Interest rate		5.00%
Term Loan [Member] \| 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, borrowings		$ 20,000,000

Indebtedness (Future Maturities

Indebtedness (Future Maturities On Debt) (Details) $ in Thousands	Dec. 31, 2019USD ($)
Indebtedness [Abstract]
2021	$ 14,634
2022	17,561
2023	17,561
2024	10,244
Total long-term debt, of which $0 is current and $60,000 is noncurrent	60,000
Noncurrent	$ 60,000

Leases (Narrative) (Details)

Leases (Narrative) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018	Oct. 31, 2015
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets	$ 4,032
Operating lease liabilities	$ 2,796
Operating Lease, Weighted Average Remaining Lease Term	3 years 6 months
Finance Lease, Weighted Average Remaining Lease Term	11 years
Operating Lease, Weighted Average Discount Rate, Percent	5.90%
Finance Lease, Weighted Average Discount Rate, Percent	7.00%
Accounting Standards Update 2018-11 Leases (Topic 842): Targeted Improvements [Member]
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets		$ 1,884
Operating lease liabilities		$ 2,189
ASC 842 [Member]
Lessee, Lease, Description [Line Items]
Accrued rent			$ 305
Minimum [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Term of Contract	1 year
Lessee, Finance Lease, Term of Contract	1 year
Maximum [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Term of Contract	11 years
Lessee, Finance Lease, Term of Contract	11 years
Letter of Credit [Member] \| Mason Lease [Member]
Lessee, Lease, Description [Line Items]
Letter of credit outstanding				$ 1,250

Leases (Summary Of Components O

Leases (Summary Of Components Of Lease Expense) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)
Leases [Abstract]
Operating lease cost	$ 952
Amortization of right-of-use assets	998
Interest on lease liabilities	872
Total finance lease cost	$ 1,870

Leases (Summary Of Supplemental

Leases (Summary Of Supplemental Cash Flow Information Related To Leases) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)
Leases [Abstract]
Operating cash flows from operating leases	$ 1,026
Operating cash flows from finance leases	872
Financing cash flows from finance leases	629
Operating Leases	1,884
Finance Leases	270
Operating lease right-of-use asset obtained in business combination	$ 2,929

Leases (Summary Of Supplement_2

Leases (Summary Of Supplemental Balance Sheet Information Related To Leases) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Leases [Abstract]
Operating lease right-of-use assets	$ 4,032
Other current liabilities and current maturities of leases and long-term debt	(1,465)
Operating lease liabilities	(2,796)
Total operating lease liabilities	(4,261)
Property and equipment, at cost	65,708	$ 54,353
Finance Leases, Property and equipment, at cost	14,733
Finance Leases, Accumulated depreciation	(4,197)
Finance Leases, Property and equipment, net	10,536
Accumulated depreciation	(33,062)	(27,273)
Property and equipment, net	32,646	27,080
Other current liabilities and current maturities of leases and long-term debt	(753)
Finance lease liabilities	(11,774)	$ (12,172)
Total finance lease liabilities	$ (12,527)

Leases (Schedule Of Maturities

Leases (Schedule Of Maturities Of Lease Liabilities) (Details) $ in Thousands	Dec. 31, 2019USD ($)
Leases [Abstract]
2020	$ 1,465
2021	1,337
2022	1,178
2023	708
Total payments	4,688
Less imputed interest	(427)
Total	4,261
2020	1,597
2021	1,602
2022	1,623
2023	1,646
2024	1,670
2025 and thereafter	9,799
Total payments	17,937
Less imputed interest	(5,410)
Total	$ 12,527

Commitments and Contingencies (

Commitments and Contingencies (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Commitments and Contingencies [Line Items]
Royalty expense	$ 2,892	$ 2,715	$ 2,323
Minimum [Member]
Commitments and Contingencies [Line Items]
Royalty rates	3.00%
Royalty agreement term	2023
Maximum [Member]
Commitments and Contingencies [Line Items]
Royalty rates	5.00%
Royalty agreement term	2025

Revenue (Narrative) (Details)

Revenue (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
Revenue (Narrative) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Revenue	$ 61,321	$ 56,614	$ 58,906	$ 53,966	$ 52,893	$ 49,941	$ 51,802	$ 46,994	$ 230,807	$ 201,630	$ 174,716
Shipping and Handling [Member]
Disaggregation of Revenue [Line Items]
Revenue									$ 1,485	$ 1,236	$ 1,090

Income Taxes (Narrative) (Detai

Income Taxes (Narrative) (Details) - USD ($)	12 Months Ended
Income Taxes (Narrative) (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019	Jan. 01, 2017	Dec. 31, 2016
Income Tax Contingency [Line Items]
Research and development and AMT credit carryforwards, net	$ 8,193,000	$ 6,206,000
Pre-tax book loss for domestic operations	(28,002,000)	(13,443,000)	$ (19,409,000)
Pre-tax book loss for international operations	(6,993,000)	(7,468,000)	(7,469,000)
Undistributed earnings of foreign subsidiaries	304,000
Unrecognized deferred tax assets					$ 2,816,000
Finance and operating lease liabilities	4,016,000
Right-of-use assets	(3,476,000)
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
Unrecognized tax benefits	1,777,000	$ 1,157,000	$ 1,157,000			$ 3,175,000
Unrecognized tax benefits that would result in adjustments to other tax accounts	$ 1,777,000
Tax Year 2015 [Member]
Income Tax Contingency [Line Items]
Open Tax Year	2015
Tax Year 2016 [Member]
Income Tax Contingency [Line Items]
Open Tax Year	2016
Federal [Member]
Income Tax Contingency [Line Items]
Operating loss carryforward	$ 80,101,000
Research and development and AMT credit carryforwards, net	8,168,000
Federal [Member] \| Tax Year 2021 And 2038 [Member]
Income Tax Contingency [Line Items]
Operating loss carryforward	340,079,000
State [Member]
Income Tax Contingency [Line Items]
Operating loss carryforward	260,924,000
Foreign [Member]
Income Tax Contingency [Line Items]
Operating loss carryforward	$ 42,712,000
Minimum [Member] \| Federal [Member]
Income Tax Contingency [Line Items]
Operating loss carryforward, expiration year	2021
Research and development credit credit carryforwards expiration year	2023
Minimum [Member] \| State [Member]
Income Tax Contingency [Line Items]
Operating loss carryforward, expiration year	2020
Minimum [Member] \| Foreign [Member]
Income Tax Contingency [Line Items]
Operating loss carryforward, expiration year	2020
Maximum [Member] \| Federal [Member]
Income Tax Contingency [Line Items]
Operating loss carryforward, expiration year	2038
Research and development credit credit carryforwards expiration year	2040
Maximum [Member] \| State [Member]
Income Tax Contingency [Line Items]
Operating loss carryforward, expiration year	2040
Maximum [Member] \| Foreign [Member]
Income Tax Contingency [Line Items]
Operating loss carryforward, expiration year	2028
SentreHEART [Member]
Income Tax Contingency [Line Items]
Net deferred tax assets	$ 20,590,000
ASC 842 [Member]
Income Tax Contingency [Line Items]
Finance and operating lease liabilities				$ 400,000
Right-of-use assets				$ 400,000

Income Taxes (Summary Of Compan

Income Taxes (Summary Of Company's Provision for Income Taxes) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current Tax Expense
Federal	$ (26)	$ (51)
State	34	28	$ 44
Foreign	165	198	72
Total current tax expense	173	175	116
Deferred Tax Expense
Federal	(7,655)	(3,048)	18,485
State	(1,368)	178	(1,337)
Foreign	(1,690)	45	(2,241)
Change in valuation allowance	10,739	2,876	(15,009)
Total deferred tax expense	26	51	(102)
Total tax expense	$ 199	$ 226	$ 14

Income Taxes (Summary Of Detail

Income Taxes (Summary Of Detail Of Deferred Tax Assets And Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets (liabilities):
Net operating loss carryforward	$ 111,000	$ 68,563
Research and development and AMT credit carryforwards, net	8,193	6,206
Deferred interest	909	774
Equity compensation	8,233	4,750
Accruals and reserves	3,513	802
Inventories	1,007	726
Intangible assets	(30,996)	(11,448)
Property and equipment, net	(1,482)	(608)
Finance and operating lease liabilities	4,016
Right-of-use assets	(3,476)
Other, net	287	135
Subtotal	101,204	69,900
Less valuation allowance	(101,178)	(69,849)
Total	$ 26	$ 51

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, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Taxes [Abstract]
Federal tax at statutory rate	21.00%	21.00%	34.00%
Federal and Foreign tax rate change	1.40%	(6.84%)	(109.68%)
Federal R&D credit	2.53%	4.39%	(0.40%)
Federal deferred adjustment	3.28%	(10.77%)
Federal NOL adjustment for ASU			10.48%
Valuation allowance	(32.45%)	(13.75%)	55.84%
State income taxes	4.02%	(0.99%)	4.81%
Foreign NOL rate change	(1.17%)	(1.22%)	1.30%
Foreign tax rate differential	(0.38%)	(0.60%)	(2.45%)
Permanent differences and other	1.17%	7.70%	6.05%
Effective tax rate	(0.60%)	(1.08%)	(0.05%)
Federal tax at statutory rate	$ (6,950)	$ (4,391)	$ (9,139)
Federal and Foreign tax rate change	(462)	1,430	29,480
Federal R&D credit	(837)	(918)	107
Federal deferred adjustment	(1,085)	2,253
Federal NOL adjustment for ASU			(2,816)
Valuation allowance	10,739	2,876	(15,009)
State income taxes	(1,334)	206	(1,292)
Foreign NOL rate change	388	256	(348)
Foreign tax rate differential	126	125	658
Permanent differences and other	(386)	(1,611)	(1,627)
Total tax expense	$ 199	$ 226	$ 14

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, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Taxes [Abstract]
Balance at the beginning of the year	$ 1,157	$ 1,157	$ 3,175
Increases (decreases) for prior year tax positions	620
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	$ 1,777	$ 1,157	$ 1,157

Concentrations (Narrative) (Det

Concentrations (Narrative) (Details) $ in Thousands	12 Months Ended
Concentrations (Narrative) (Details) $ in Thousands	Dec. 31, 2019USD ($)customer	Dec. 31, 2018	Dec. 31, 2017
Concentration Risk [Line Items]
Number of customers \| customer	10
Cash and cash equivalents balance in excess of FDIC limits \| $	$ 28,096
Net Revenue [Member]
Concentration Risk [Line Items]
Percentage representation of significant customer	12.00%	10.80%	13.20%
Customer Concentration Risk [Member] \| Accounts Receivable [Member]
Concentration Risk [Line Items]
Percentage representation of significant customer	16.50%	11.80%

Employee Benefit Plans (Narrati

Employee Benefit Plans (Narrative) (Details) - USD ($)	12 Months Ended
Employee Benefit Plans (Narrative) (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
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	$ 1,915,000	$ 1,560,000	$ 1,367,000
Discretionary contributions made	0	0	0
Total contributions to retirement plan	$ 248,000	$ 243,000	$ 205,000

Equity Compensation Plans (Narr

Equity Compensation Plans (Narrative) (Details) - USD ($)	12 Months Ended
Equity Compensation Plans (Narrative) (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total intrinsic value of options exercised	$ 1,985,000	$ 5,343,000	$ 5,121,000
Tax benefit recognized	$ 0	$ 0	0
Employee Stock Option [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 9 months 18 days
Options awarded	42,000	52,000
Stock options compensation costs	$ 997,000
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average period of recognizing cost	1 year 8 months 12 days
Total fair value of restricted stock vested	$ 23,479,000	$ 11,864,000	$ 6,235,000
Unrecognized compensation costs related to non-vested performance options	$ 16,974,000
Performance Shares [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 7 months 6 days
Options awarded
Number of shares options vest in	25,000
Period of considering closing price of common stock	30 days
Stock options compensation costs	$ 6,625,000
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	$ 17,971,000
Performance Share Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting right of shares of common stock	1
President And CEO [Member] \| Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options awarded	450,000
Minimum [Member] \| Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Contractual term (years)	5 years 1 month 17 days	5 years 1 month 20 days	5 years 2 months 15 days
Expected volatility of stock	40.00%	41.00%	43.00%
Interest rate	1.43%	2.31%	1.75%
Minimum [Member] \| Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	1 year
Maximum [Member] \| Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Contractual term (years)	5 years 8 months 8 days	5 years 8 months 15 days	5 years 9 months 3 days
Expected volatility of stock	42.00%	42.00%	48.00%
Interest rate	2.64%	3.01%	2.12%
Maximum [Member] \| Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	4 years
2014 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance	11,999,000
Shares available for future grants	1,578,000
2014 Plan [Member] \| Employee Stock Option [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]
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	3,000
Offering period	6 months
Shares available for future issuance under the ESPP	491,000
2018 PSAs [Member] \| Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
2018 PSAs [Member] \| Minimum [Member] \| Performance Shares [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 Shares [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] \| Employee Stock Option [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	33.30%
Tranche 4 [Member] \| Performance Shares [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 Shares [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 Shares [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 Shares [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 Shares [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 Shares [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, 2019	Dec. 31, 2018	Dec. 31, 2017
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning balance, Number of Shares Outstanding, Stock Options	1,582	2,026
Granted, Number of Shares Outstanding, Stock Options	42	52
Exercised, Number of Shares Outstanding, Stock Options	(110)	(474)
Cancelled or forfeited, Number of Shares Outstanding, Stock Options	(7)	(22)
Ending balance, Number of Shares Outstanding, Stock Options	1,507	1,582	2,026
Vested and expected to vest, Number of Shares Outstanding, Stock Options	1,503	1,574
Exercisable, Ending balance, Number of Shares Outstanding, Stock Options	1,392	1,419
Beginning balance, Weighted Average Exercise Price, Stock Options	$ 13.83	$ 13.30
Granted, Weighted Average Exercise Price, Stock Options	28.77	26.05
Exercised, Weighted Average Exercise Price, Stock Options	10.91	12.70
Cancelled or forfeited, Weighted Average Exercise Price, Stock Options	30.48	18.14
Ending balance, Weighted Average Exercise Price, Stock Options	14.38	13.83	$ 13.30
Vested and expected to vest, Weighted Average Exercise Price, Stock Options	14.35	13.78
Exercisable, Ending balance, Weighted Average Exercise Price, Stock Options	$ 13.55	$ 12.99
Outstanding, Ending balance, Weighted Average Remaining Contractual Term, Stock Options	4 years 3 months	5 years 7 days
Vested and expected to vest, Weighted Average Remaining Contractual Term, Stock Options	4 years 2 months 26 days	5 years
Exercisable, Ending balance, Weighted Average Remaining Contractual Term, Stock Options	3 years 10 months 24 days	4 years 7 months 17 days
Outstanding, Ending balance, Aggregate Intrinsic Value, Stock Options	$ 27,340	$ 26,587
Vested and expected to vest, Aggregate Intrinsic Value, Stock Options	27,319	26,525
Exercisable, Ending balance, Aggregate Intrinsic Value, Stock Options	$ 26,398	$ 24,991
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning balance, Number of Shares Outstanding	1,746	1,845
Awarded, Number of Shares Outstanding	435	630
Released, Number of Shares Outstanding	(776)	(638)
Forfeited, Number of Shares Outstanding	(3)	(91)
Ending balance, Number of Shares Outstanding	1,402	1,746	1,845
Beginning balance, Weighted Average Grant Date Fair Value	$ 18.19	$ 18.22
Awarded, Weighted Average Grant Date Fair Value	30.12	18.71	$ 19.38
Released, Weighted Average Grant Date Fair Value	18.44	18.87
Forfeited, Weighted Average Grant Date Fair Value	18.02	17.97
Ending balance, Weighted Average Grant Date Fair Value	$ 21.76	$ 18.19	$ 18.22
Performance Share Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning balance, Number of Shares Outstanding	90
Awarded, Number of Shares Outstanding	174	90
Released, Number of Shares Outstanding
Forfeited, Number of Shares Outstanding
Ending balance, Number of Shares Outstanding	264	90
Beginning balance, Weighted Average Grant Date Fair Value	$ 17.71
Awarded, Weighted Average Grant Date Fair Value	30.77	$ 17.71
Released, Weighted Average Grant Date Fair Value
Forfeited, Weighted Average Grant Date Fair Value
Ending balance, Weighted Average Grant Date Fair Value	$ 26.34	$ 17.71
Performance Shares [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	350
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	3 years 5 months 12 days	4 years 5 months 12 days
Exercisable, Ending balance, Weighted Average Remaining Contractual Term, Stock Options	3 years 5 months 12 days	4 years 5 months 12 days
Outstanding, Ending balance, Aggregate Intrinsic Value, Stock Options	$ 8,566	$ 5,555
Exercisable, Ending balance, Aggregate Intrinsic Value, Stock Options	$ 6,662	$ 4,321

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, 2019	Dec. 31, 2018	Dec. 31, 2017
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total	$ 17,977	$ 16,495	$ 14,615
Cost of Revenue [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total	917	1,545	610
Research and Development Expenses [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total	2,374	1,987	2,052
Selling, General and Administrative Expenses [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total	14,686	12,963	11,953
Restricted Stock Awards & Time-Based Stock Options [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total	13,922	15,032	13,908
Performance Share Awards [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total	3,254	766
Performance Shares [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total			43
ESPP [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total	$ 801	$ 697	$ 664

Equity Compensation Plans (Assu

Equity Compensation Plans (Assumptions Used for Determining Fair Value of Options) (Details) - Employee Stock Option [Member]	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average volatility	40.87%	41.51%	44.50%
Dividend yield	0.00%	0.00%	0.00%
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of risk-free interest rate	1.43%	2.31%	1.75%
Range of expected life of stock option (years)	5 years 1 month 17 days	5 years 1 month 20 days	5 years 2 months 15 days
Range of expected volatility of stock	40.00%	41.00%	43.00%
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of risk-free interest rate	2.64%	3.01%	2.12%
Range of expected life of stock option (years)	5 years 8 months 8 days	5 years 8 months 15 days	5 years 9 months 3 days
Range of expected volatility of stock	42.00%	42.00%	48.00%

Equity Compensation Plans (Weig

Equity Compensation Plans (Weighted Average Estimated Grant Date Fair Value Per Share of Stock Options, Restricted Stock Granted, And Performance Awards) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Employee Stock Option [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	$ 11.56	$ 10.97	$ 8.60
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average estimated grant date fair value per share of the restricted stock granted	30.12	18.71	$ 19.38
Performance Share 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	$ 30.77	$ 17.71

Equity Compensation Plans (Esti

Equity Compensation Plans (Estimated Grant Date Fair Value Per Share of Performance Options Granted) (Details) - Performance Shares [Member]	12 Months Ended
	Dec. 31, 2019$ / 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

Segment and Geographic Inform_3

Segment and Geographic Information (Narrative) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Europe [Member]
Long-lived assets	$ 1,228	$ 1,296

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, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue recognized from contracts with customers	$ 61,321	$ 56,614	$ 58,906	$ 53,966	$ 52,893	$ 49,941	$ 51,802	$ 46,994	$ 230,807	$ 201,630	$ 174,716
Revenue	$ 61,321	$ 56,614	$ 58,906	$ 53,966	$ 52,893	$ 49,941	$ 51,802	$ 46,994	230,807	201,630	174,716
United States [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue recognized from contracts with customers									185,829	162,146	138,387
Revenue									185,829	162,146	138,387
Europe [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue recognized from contracts with customers									27,929	25,912	21,901
Revenue									27,929	25,912	21,901
Asia [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue recognized from contracts with customers									15,976	12,687	13,616
Revenue									15,976	12,687	13,616
Other International [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue recognized from contracts with customers									1,073	885	812
Revenue									1,073	885	812
International [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue recognized from contracts with customers									44,978	39,484	36,329
Revenue									$ 44,978	$ 39,484	$ 36,329

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, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue from External Customer [Line Items]
Revenue	$ 61,321	$ 56,614	$ 58,906	$ 53,966	$ 52,893	$ 49,941	$ 51,802	$ 46,994	$ 230,807	$ 201,630	$ 174,716
United States [Member]
Revenue from External Customer [Line Items]
Revenue									185,829	162,146	138,387
United States [Member] \| Open-heart Ablation [Member]
Revenue from External Customer [Line Items]
Revenue									80,205	72,250	64,517
United States [Member] \| Minimally Invasive Ablation [Member]
Revenue from External Customer [Line Items]
Revenue									34,842	35,053	34,421
United States [Member] \| Appendage Management [Member]
Revenue from External Customer [Line Items]
Revenue									68,166	52,891	37,281
United States [Member] \| Ablation And Appendage Management [Member]
Revenue from External Customer [Line Items]
Revenue									183,213	160,194	136,219
United States [Member] \| Valve Tools [Member]
Revenue from External Customer [Line Items]
Revenue									2,616	1,952	2,168
International [Member]
Revenue from External Customer [Line Items]
Revenue									44,978	39,484	36,329
International [Member] \| Open-heart Ablation [Member]
Revenue from External Customer [Line Items]
Revenue									24,945	21,118	20,718
International [Member] \| Minimally Invasive Ablation [Member]
Revenue from External Customer [Line Items]
Revenue									8,349	9,176	8,007
International [Member] \| Appendage Management [Member]
Revenue from External Customer [Line Items]
Revenue									11,476	8,988	7,251
International [Member] \| Ablation And Appendage Management [Member]
Revenue from External Customer [Line Items]
Revenue									44,770	39,282	35,976
International [Member] \| Valve Tools [Member]
Revenue from External Customer [Line Items]
Revenue									$ 208	$ 202	$ 353

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, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating Results:
Revenue recognized from contracts with customers	$ 61,321	$ 56,614	$ 58,906	$ 53,966	$ 52,893	$ 49,941	$ 51,802	$ 46,994	$ 230,807	$ 201,630	$ 174,716
Gross profit	44,774	41,797	43,893	39,871	38,590	35,948	38,079	34,503	170,335	147,120	126,163
Loss from operations	(15,326)	(8,637)	(3,839)	(5,320)	(2,607)	(6,048)	958	(9,430)	(33,122)	(17,127)	(24,979)
Net loss	$ (16,096)	$ (9,362)	$ (4,101)	$ (5,635)	$ (3,430)	$ (7,235)	$ (338)	$ (10,134)	$ (35,194)	$ (21,137)	$ (26,892)
Net loss per share (basic and diluted)	$ (0.42)	$ (0.25)	$ (0.11)	$ (0.15)	$ (0.09)	$ (0.22)	$ (0.01)	$ (0.31)

Schedule II (Schedule Of Valuat

Schedule II (Schedule Of Valuation And Qualifying Accounts) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reserve For Sales Returns And Allowances [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance		$ 1,410	$ 1,169	$ 834
Additions		369	312	441
Other	[1]	2,240
Deductions		40	71	106
Ending Balance		3,979	1,410	1,169
Allowance For Inventory Valuation [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance		1,029	889	1,080
Additions		848	718	1,004
Other	[1]
Deductions		360	578	1,195
Ending Balance		1,517	1,029	889
Valuation Allowance For Deferred Tax Assets [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance		69,849	66,973	81,982
Additions		10,739	2,876
Other	[1]	20,590
Deductions				15,009
Ending Balance		$ 101,178	$ 69,849	$ 66,973

[1]	In connection with the acquisition of SentreHEART, the Company recognized an allowance for sales returns and refunds of for transition to ASC 606 to reflect SentreHEART’s historical refund practices, and recorded an offsetting valuation allowance for deferred tax assets.