AtriCure (ATRC) 10-Q 27 Apr 18 2018 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2018	Apr. 24, 2018
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q1
Trading Symbol	ATRC
Entity Registrant Name	AtriCure, Inc.
Entity Central Index Key	1,323,885
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		35,040,049

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 21,229	$ 21,809
Short-term investments	14,809	12,642
Accounts receivable, less allowance for doubtful accounts of $32 and $32	22,325	23,083
Inventories	22,571	22,451
Other current assets	3,835	2,273
Total current assets	84,769	82,258
Property and equipment, net	28,549	28,749
Intangible assets, net	50,422	50,764
Goodwill	105,257	105,257
Other noncurrent assets	705	676
Total Assets	269,702	267,704
Current liabilities:
Accounts payable	11,583	12,431
Accrued liabilities	14,714	18,911
Other current liabilities and current maturities of capital leases	575	561
Total current liabilities	26,872	31,903
Capital leases	12,626	12,761
Long-term debt	39,313	24,100
Other noncurrent liabilities	37,768	37,774
Total Liabilities	116,579	106,538
Commitments and contingencies (Note 10)
Stockholders' Equity:
Common stock, $0.001 par value, 90,000 shares authorized and 35,039 and 34,586 issued and outstanding	35	35
Additional paid-in capital	388,976	386,963
Accumulated other comprehensive income	112	34
Accumulated deficit	(236,000)	(225,866)
Total Stockholders' Equity	153,123	161,166
Total Liabilities and Stockholders' Equity	$ 269,702	$ 267,704

Condensed Consolidated Balance3

Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Condensed Consolidated Balance Sheets [Abstract]
Accounts receivable, allowance for doubtful accounts	$ 32	$ 32
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	90,000,000	90,000,000
Common stock, shares issued	35,039,000	34,586,000
Common stock, shares outstanding	35,039,000	34,586,000

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Condensed Consolidated Statements of Operations and Comprehensive Loss [Abstract]
Revenue	$ 46,994	$ 41,273
Cost of revenue	12,491	11,265
Gross profit	34,503	30,008
Operating expenses:
Research and development expenses	9,057	9,550
Selling, general and administrative expenses	34,876	30,100
Total operating expenses	43,933	39,650
Loss from operations	(9,430)	(9,642)
Other income (expense):
Interest expense	(820)	(554)
Interest income	76	54
Other	88	(18)
Loss before income tax expense	(10,086)	(10,160)
Income tax expense	48	23
Net loss	$ (10,134)	$ (10,183)
Basic and diluted net loss per share	$ (0.31)	$ (0.32)
Weighted average shares outstanding — basic and diluted	32,926	32,020
Comprehensive loss:
Unrealized (loss) gain on investments	$ (8)	$ 2
Foreign currency translation adjustment	86	73
Other comprehensive income	78	75
Net loss	(10,134)	(10,183)
Comprehensive loss, net of tax	$ (10,056)	$ (10,108)

Condensed Consolidated Stateme5

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash flows from operating activities:
Net loss	$ (10,134)	$ (10,183)
Adjustments to reconcile net loss to net cash used in operating activities:
Share-based compensation expense	3,890	3,628
Depreciation	1,857	1,962
Amortization of intangible assets	342	342
Amortization of deferred financing costs	93	66
(Gain) loss on disposal of property and equipment	(5)	62
Realized (gain) loss from foreign exchange on intercompany transactions	(82)	21
(Accretion) amortization of investments	(15)	38
Change in allowance for doubtful accounts	51	(136)
Changes in operating assets and liabilities:
Accounts receivable	783	(397)
Inventories	(43)	(1,145)
Other current assets	(1,540)	(1,175)
Accounts payable	(408)	353
Accrued liabilities	(4,244)	(2,827)
Other noncurrent assets and liabilities	21	(155)
Net cash used in operating activities	(9,434)	(9,546)
Cash flows from investing activities:
Purchases of available-for-sale securities	(10,359)	(3,096)
Sales and maturities of available-for-sale securities	8,200	10,550
Purchases of property and equipment	(2,086)	(1,728)
Net cash (used in) provided by investing activities	(4,245)	5,726
Cash flows from financing activities:
Proceeds from debt borrowings	17,381
Payments on debt and capital leases	(1,326)	(120)
Payment of debt fees	(1,114)
Proceeds from stock option exercises	1,787	631
Shares repurchased for payment of taxes on stock awards	(3,665)	(1,735)
Net cash provided by (used in) financing activities	13,063	(1,224)
Effect of exchange rate changes on cash and cash equivalents	36	(10)
Net decrease in cash and cash equivalents	(580)	(5,054)
Cash and cash equivalents-beginning of period	21,809	24,208
Cash and cash equivalents-end of period	21,229	19,154
Supplemental cash flow information:
Cash paid for interest	416	488
Cash paid for income taxes
Non-cash investing and financing activities:
Accrued purchases of property and equipment	178	559
Assets acquired through capital lease	27
Capital lease asset early termination	$ (9)

Description of Business and Sum

Description of Business and Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2018
Description of Business and Summary of Significant Accounting Policies [Abstract]
Description of Business and Summary of Significant Accounting Policies	1. DESC RIPTION 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. All intercompany accounts and transactions have been eliminated in consolidation. 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. Basis of Presentation —The accompanying interim financial statements have been prepared in accordance with the rules and regulations of the Securities and Exchange Commission (SEC). The accompanying interim financial statements are unaudited, but in the opinion of the Company’s management, contain all normal, recurring adjustments considered necessary to present fairly the financial position, results of operations and cash flows for the periods presented in conformity with accounting principles generally accepted in the United States of America (GAAP) applicable to interim periods. Certain information and footnote disclosures included in annual financial statements prepared in accordance with GAAP have been omitted or condensed. The Company believes the disclosures herein are adequate to make the information presented not misleading. Results of operations are not necessarily indicative of the results expected for the full year or for any future period. The accompanying Condensed Consolidated Financial Statements should be read in conjunction with the audited financial statements of the Company included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017 filed with the SEC. 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 in the accompanying Condensed Consolidated Financial Statements. Investments —The Company invests primarily in U.S. Government agencies and securities, corporate bonds, commercial paper and asset-backed securities and classifies all investments as available-for-sale. Investments with maturities of less than one year are classified as short-term investments. Investments are recorded at fair value, with unrealized gains and losses recorded as accumulated other comprehensive income. Gains and losses are recognized using the specific identification method when securities are sold and are included in interest income or expense in the Condensed Consolidated Statements of Operations and Comprehensive Loss. 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 8 for further discussion on revenue. Sales Returns and Allowances —The Company maintains a provision for sales returns and allowances for potential returns of defective or damaged products and products shipped in error and invoice adjustments. The Company adjusts the provision quarterly using a combination of specific identification and an estimated general reserve based on historical experience. Increases to the provision result in a reduction of revenue. The provision is included in accrued liabilities in the Condensed Consolidated Balance Sheets. Allowance for Doubtful Accounts Receivable —The Company evaluates the collectability of accounts receivable to determine the appropriate allowance for doubtful accounts. In determining the amount of the allowance, the Company considers aging of accounts, historical credit losses, customer-specific information and other relevant factors. Increases to the allowance result in an increase in selling, general and administrative expenses. The Company reviews accounts and adjusts the allowance based on current circumstances and charges off uncollectible receivables against the allowance when all attempts to collect the receivable have failed. The Company’s history of write-offs against the allowance has not been significant. Inventories —Inventories are stated at the lower of cost or net realizable value based on the first-in, first-out cost method (FIFO). The Company’s industry is characterized by rapid product development and frequent new product introductions. Uncertain timing of product approvals, variability in product launch strategies and variation in product use all impact inventory reserves for excess, obsolete and expired products. An estimated inventory reserve for excess, obsolete and expired inventory is recorded quarterly. Increases to inventory reserves result in an increase in cost of revenue. Inventories are written off against the reserve when they are physically disposed. Inventories consist of the following:      March 31, December 31,  2018 2017  Raw materials $ 8,804 $ 7,755  Work in process 1,803 1,299  Finished goods 11,964 13,397  Inventories $ 22,571 $ 22,451 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. The estimated useful life by major asset category is the following:      Estimated Useful Life  Generators and related equipment 1 - 3 years  Building under capital lease 15 years  Computers, software and office equipment 3 years  Machinery and equipment 3 - 7 years  Furniture and fixtures 3 - 7 years  Leasehold improvements 5 - 15 years  Equipment under capital leases 3 - 5 years 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 radiofrequency (RF) and cryo generators are generally placed with customers that use the Company’s disposable products. The estimated useful lives of generators are based on anticipated usage by customers and may change in future periods with changes in usage or introduction of new technologies. Depreciation related to generators and related equipment, which is recorded in cost of revenue in the Condensed Consolidated Statements of Operations and Comprehensive Loss, was $827 and $916 for the three months ended March 31, 2018 and 2017 . As of March 31, 2018 and December 31, 2017 , the net carrying value of generators and related equipment included in net property and equipment in the Condensed Consolidated Balance Sheets was $4,754 and $4,656 . The Company at least annually reviews property and equipment for impairment using its best estimates based on reasonable and supportable assumptions and 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. Intangible assets include In Process Research and Development (IPR&D), which represents the value of technology acquired in business combinations that has not yet reached technological feasibility. The primary basis for determining technological feasibility is obtaining specific regulatory approval. 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, IPR&D will be amortized over its estimated useful life. If the IPR&D project is abandoned, the IPR&D would be written off. IPR&D represents an estimate of the fair value of the pre-market approval (PMA) that could result from the CONVERGE IDE clinical trial. The Company at least annually reviews intangible assets for impairment using its best estimates based on reasonable and supportable assumptions and projections. Goodwill— Goodwill represents the excess of purchase price over the fair value of the net assets acquired in business combinations. The Company has historically tested goodwill for impairment annually on November 30, or more often if impairment indicators are present. The Company’s goodwill is accounted for in a single reporting unit representing the Company as a whole. Other Noncurrent Liabilities— Other noncurrent liabilities consist of contingent consideration recorded in business combinations and other contractual obligations. Although the Company expects to settle a portion of the contingent consideration liability in 2018, the balance is included in noncurrent liabilities as such settlement is both required and expected to be made in shares of the Company’s common stock pursuant to the nContact Surgical, Inc. (nContact) merger agreement. Other Income (Expense) — Other income (expense) consists primarily 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 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, taxable income in carry-back years 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. Net Loss Per Share —As required under GAAP, 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 4,216 and 4,580 stock options, restricted stock shares, restricted stock units and performance award shares as of March 31, 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 Loss and Accumulated Other Comprehensive Income —In addition to net losses, the comprehensive loss includes foreign currency translation adjustments and unrealized losses on investments. Accumulated other comprehensive income (loss) consisted of the following (net of tax):      Three Months Ended  March 31,  2018 2017  Total accumulated other comprehensive income (loss) at beginning of period $ 34 $ (468)  Unrealized Losses on Investments  Balance at beginning of period $ (6) $ (21)  Other comprehensive (loss) income before reclassifications (8) 2  Amounts reclassified from accumulated other comprehensive income (loss) to other income (loss) — —  Balance at end of period $ (14) $ (19)  Foreign Currency Translation Adjustment  Balance at beginning of period $ 40 $ (447)  Other comprehensive income before reclassifications 168 52  Amounts reclassified from accumulated other comprehensive income (loss) to other income (loss) (82) 21  Balance at end of period $ 126 $ (374)  Total accumulated other comprehensive income (loss) at end of period $ 112 $ (393) 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 and regulatory affairs. Advertising Costs — The Company expenses advertising costs as incurred. Advertising costs were not significant during the three months ended March 31, 2018 and 2017 . Share-Based Compensation —As required under GAAP, the Company records share-based compensation for all employee share-based payment awards, including stock options, restricted stock, restricted stock units, performance shares and stock purchases related to an employee stock purchase plan, based on estimated fair values. The Company recognized share-based compensation expense of $3,890 and $3,628 for the three months ended March 31, 2018 and 2017 . The fair value of share-based payment awards is estimated on the date of grant using an option-pricing model. The value of the portion of the award that is ultimately expected to vest, net of estimated forfeitures, is recognized as expense over the service periods in the Company’s Condensed Consolidated Statements of Operations and Comprehensive Loss. The Company estimates forfeitures at the time of grant and revises them 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 a number of subjective variables. These variables include, but are not limited to, the Company’s expected stock price volatility over the term of the awards and actual and projected employee stock option exercise behaviors. The fair value of market-based performance option grants is estimated at the date of grant using a Monte-Carlo simulation. The value of the portion of the awards that is ultimately expected to vest is recognized as expense over the service periods in the Condensed Consolidated Statements of Operations and Comprehensive Loss. The Company estimates the fair value of restricted stock, restricted stock units and performance shares based upon the grant date closing market price of the Company’s common stock. The Company also has an employee stock purchase plan (ESPP) which is available to all eligible employees as defined by the plan document. Under the ESPP, shares of the Company’s common stock may be purchased at a discount. The Company estimates the number of shares to be purchased under the ESPP at the beginning of each purchase period based upon the fair value of the stock at the beginning of the purchase period using the Black-Scholes model and records estimated compensation expense during the period. Expense is trued up to actual at the time of stock purchase. Use of Estimates —The preparation of the financial statements in conformity with 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.

Recent Accounting Pronouncement

Recent Accounting Pronouncements	3 Months Ended
	Mar. 31, 2018
Recent Accounting Pronouncements [Abstract]
Recent Accounting Pronouncements	2. RECENT ACCOUNTING PRONOUNCEMENTS In May 2014 , the FASB issued Accounting Standards Update (ASU) 2014-09, “ Revenue from Contracts with Customers” (ASU 2014-09), which requires an entity to recognize revenue for the transfer of goods or services equal to the amount that it expects to be entitled in exchange for those goods or services. ASU 2014-09 supersedes most previous revenue recognition guidance and is effective for interim and annual reporting periods beginning within 2018. The Company adopted the new guidance as of January 1, 2018 using the modified retrospective adoption method. See Note 8 for further details. In February 2016 , the FASB issued ASU 2016-02, “Leases” (ASU 2016-02) which requires lessees to record most leases onto their balance sheet but recognize expenses on their income statement in a manner similar to today’s accounting. The guidance is effective for interim and annual reporting periods beginning within 2019 . Entities are required to use a modified retrospective approach for leases that exist or are entered into after the beginning of the earliest comparative period in the financial statements. Full retrospective application is prohibited. The Company is evaluating the provisions of ASU 2016-02 to determine the impact on its consolidated financial position, results of operations and related disclosures. In February 2018, the FASB issued ASU 2018-02, “Reclassification of Certain Tax Effects From Accumulated Other Comprehensive Income (AOCI)” (ASU 2018-02) to address industry concerns related to the application of ASC 740, “Income Taxes” to certain provisions of the new tax reform legislation. Upon adopting ASU 2018-02, an entity is required to disclose (1) its accounting policy related to releasing income tax effects from AOCI, (2) whether it has elected to reclassify, to retained earnings in the statement of stockholders’ equity, the stranded tax effects in AOCI related to the new tax reform legislation and (3) if it has elected to reclassify to retained earnings the stranded tax effects in AOCI related to the new tax reform legislation, what the reclassification encompasses. The guidance is effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. Early adoption is permitted. An entity will apply this guidance to each period in which the effect of the new tax reform legislation (or portion thereof) is recorded and may apply it either (1) retrospectively as of the date of enactment or (2) as of the beginning of the period of adoption. The Company has evaluated the impact of the provisions of ASU 2018-02 on its consolidated financial position, results of operations and related disclosures and determine d that the new guidance does not have a material impact on its financial reporting upon adoption . 

Fair Value

Fair Value	3 Months Ended
	Mar. 31, 2018
Fair Value [Abstract]
Fair Value	3. FAIR VALUE GAAP 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 f air 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 Company classifies cash and investments in U.S. government agencies and securities as Level 1 within the fair value hierarchy. Accounts receivable, short-term other assets, accounts payable and accrued liabilities are also classified as Level 1. The carrying amounts of these assets and liabilities approximate their fair value due to their relatively short-term nature. Cash equivalents and investments in corporate bonds, 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. 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 March 31, 2018 :      Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Other Unobservable Inputs (Level 3) Total  Assets:  Money market funds $ — $ 4,087 $ — $ 4,087  Commercial paper — 11,750 — 11,750  U.S. government agencies and securities 1,250 — — 1,250  Corporate bonds — 5,606 — 5,606  Asset-backed securities — 3,038 — 3,038  Total assets $ 1,250 $ 24,481 $ — $ 25,731  Liabilities:  Acquisition-related contingent consideration — — 37,098 37,098  Total liabilities $ — $ — $ 37,098 $ 37,098 There were no changes in the levels or methodology of measurement of financial assets and liabilities during the three months ended March 31, 2018 . The following table represents the Company’s fair value hierarchy for its financial assets and liabilities measured at fair value on a recurring basis as of December 31, 2017 :      Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Other Unobservable Inputs (Level 3) Total  Assets:  Money market funds $ — $ 12,774 $ — $ 12,774  Commercial paper — 7,472 — 7,472  U.S. government agencies and securities 2,999 — — 2,999  Corporate bonds — 2,920 — 2,920  Total assets $ 2,999 $ 23,166 $ — $ 26,165  Liabilities:  Acquisition-related contingent consideration — — 37,098 37,098  Total liabilities $ — $ — $ 37,098 $ 37,098 Acquisition-Related Contingent Consideration. Contingent consideration arrangements under the nContact merger agreement obligate the Company to pay certain defined amounts to former shareholders of nContact if specified milestones are met related to trial enrollment, regulatory approval and revenue targets. The Company measures contingent consideration liabil ities using unobservable inputs by applying an income approach, such as the discounted cash flow technique or the probability-weighted scenario method. Various key assumptions, such as the probability of achievement of the agreed milestones, projected revenues from acquisitions and the discount rate, are used in the determination of fair value of contingent consideration arrangements and are not observable in the market, thus representing a Level 3 measurement within the fair value hierarchy. Subsequent revisions to key assumptions, which impact the estimated fair value of contingent consideration liabilities, are reflected in the Condensed Consolidated Statements of Operations and Comprehensive Loss. Acquisition-related contingent consideration is recorded in other noncurrent liabilities in the Condensed Consolidated Balance Sheets. There were no changes in the underlying estimates or discount rate used to calculate the fair value of contingent consideration d uring the three months ended March 31, 2018 . The following table represents the Company’s Level 3 fair value measurements using significant other unobservable inputs for acquisition-related contingent consideration:        Three Months Ended Twelve Months Ended  March 31, 2018 December 31, 2017  Beginning Balance $ 37,098 $ 41,176  Amounts acquired — —  Changes in fair value included in earnings — (4,078)  Ending Balance $ 37,098 $ 37,098 

Intangible Assets

Intangible Assets	3 Months Ended
	Mar. 31, 2018
Intangible Assets [Abstract]
Intangible Assets	4. INTANGIBLE ASSETS The following table provides a summary of the Company’s intangible assets:      March 31, 2018 December 31, 2017  Estimated Useful Life Cost Accumulated Amortization Cost Accumulated Amortization  Fusion technology 10 years $ 9,242 $ 3,928 $ 9,242 $ 3,697  Clamp & probe technology 3 years 829 829 829 829  SUBTLE access technology 5 years 2,179 1,092 2,179 981  IPR&D 44,021 — 44,021 —  Total $ 56,271 $ 5,849 $ 56,271 $ 5,507 Amortization expense of intangible assets with definite lives, which excludes IPR&D, was $342 for both the three months ended March 31, 2018 and 2017 . A mortization expense of intangible assets with definite lives is projected as follows:      2018 $ 1,025 April 1, 2018 through December 31, 2018  2019 1,367  2020 1,235  2021 924  2022 925  2023 and thereafter 925  Total $ 6,401

Accrued Liabilities

Accrued Liabilities	3 Months Ended
	Mar. 31, 2018
Accrued Liabilities [Abstract]
Accrued Liabilities	5. ACCRUED LIABILITIES Accrued liabilities consisted of the following:      March 31, December 31,  2018 2017  Accrued payroll and employee-related expenses $ 5,323 $ 4,097  Accrued commissions 4,353 6,964  Accrued bonus 1,987 4,726  Sales returns and allowances 1,174 1,169  Accrued royalties 645 626  Accrued taxes and value-added taxes payable 619 634  Other accrued liabilities 613 695  Total $ 14,714 $ 18,911

Indebtedness

Indebtedness	3 Months Ended
	Mar. 31, 2018
Indebtedness [Abstract]
Indebtedness	6. INDEBTEDNESS Credit Facility. The Company has a Loan and Security Agreement (Loan Agreement) with Silicon Valley Bank (SVB). The Loan Agreement, as amended and restated effective February 23, 2018 , includes a $40,000 term loan an d a $20,000 revolving line of credit , with an option to increase the revolving line of credit by up to an additional $20,000 . Such term loan and revolving line of credit each have a five -year term , maturing or expiring , as applicable, in February 2023 . Principal payments o f the term loan are to be made ratably commencing eighteen months after the inception of the loan (September 2019) through the loan’s maturity date. If the Company meets certain conditions, as specified by the Loan A greement, the commencement of term loan principal payments may be deferred by an additional six months. The term loan accrues interest at the greater of the Prime Rate plus 3.75% or 8.25% a nd is subject to an additional 3.5% fee on the original $ 40 ,000 term loan principal payable at maturity or upon acceleration or prepayment of the term loan. The Company is accruing the 3.5 % fee over the term of the Loan Agreement. As of March 31, 2018 , the Company accrued $23 of this fee and included it in the outstanding loan balance in the Condensed Consolidated Balance Sheets. The refinancing is treated as a debt modification. F inancing costs related to the term loan of $722 are net ted against the outstanding loan balance in the Condensed Consolidated Balance Sheets and amortized ratably over the term of the Loan Agreement. The revolving line of credit is subject to an annual facility fee of 0.33% of the revolving line of credit, and any borrowings bear interest at the greater of the Prime Rate or 4.50% . Borrowing availability under the revolving credit facility is based on the lesser of $ 20 ,000 or a borrowing base calculation as defined by the Loan Agreement. As of March 31, 2018, the Company had no borrowings under the revolving credit facility and had borrowing availability of $18,750 . Financing costs related to the revolving line of credit are included in other assets in the Condensed Consolidated Balance Sheets and amortized ratably over the twelve-month period of the annual fee . The Loan Agreement contains prepayment and early termination fees and establishes a financial covenant related to sales growth, along with other customary terms and conditions similar to those in the Company’s previous agreement with SVB. Specified assets have been pledged as collateral. Capital Lease Obligations. As of March 31, 2018, the Company had capital leases for its corporate headquarters building and computer equipment that expire at various terms through 2030 . C apital lease assets are depreciated over their estimated useful lives. As of March 31, 2018 , the cost of the leased assets, both building and computer equipment, was $14,472 , and related accumul ated amortization was $2,478 . In connection with the terms of the Company’s corporate headquarters lease, a letter of credit in the amount of $1,250 was issued to the building lessor in October 2015. The letter of credit is renewed annually and remains outstanding as of March 31, 2018. Future maturities of long-term debt and capital lease obligations are projected as follows:      2018 $ 1,103 April 1, 2018 through December 31, 2018  2019 5,297  2020 12,936  2021 12,941  2022 12,965  2023 and thereafter 14,173  Total payments $ 59,415  Imputed interest (6,901)  Net long-term debt and capital lease obligations, of which $575 is current and $51,939 is noncurrent $ 52,514 

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2018
Commitments and Contingencies [Abstract]
Commitments and Contingencies	7. COMMITMENTS AND CONTINGENCIES Lease Commitments. Th e Company leases certain office and warehouse facilities under noncancelable operating leases that expire at various terms through 2022 . Royalty Agreements. The Company has certain royalty agreements in place with terms that include payment of royalties of 3% to 5% of specified product sales. The royalty agreements have effective dates as early as 2003 and terms ranging from eighteen to at least twenty years , unless terminated earlier . Royalty expense of $672 and $534 is included in cost of rev enue for the three months ended March 31, 2018 and 2017 . Purchase Agreements. The Company enters into standard purchase agreements with various suppliers in the ordinary course of business. Outstanding commitments at March 31, 2018 were not significant. Legal. The Company may, from time to time, become a party to legal proceedings. Such matters are subject to many uncertainties and to outcomes of which the financial impacts are not predictable with assurance and that may not be known for extended periods of time. When management has assessed that a loss is probable and an amount can be reasonably estimated, the Company records a liability in the Condensed Consolidated Financial Statements. Costs associated with legal proceedings could have a material adverse effect on the Company’s future consolidated results of operations, financial position, or cash flows. T he Company received a Civil Investigative Demand (CID) from the U.S. Department of Justice 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 and is working with the U.S. Department of Justice to promptly respond to the CID. However, the Company cannot predict when the investigation will be resolved, the outcome of the investigation or its potential impact on the Company. The C ompany acquired nContact Surgical, Inc. pursuant to a merger agreement dated October 4, 2015. T he 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 C ompany to deliver periodic earnout reports to a designated representative of former nContact stockholders. In response to the report delivered in February 2018 , the Company received a letter from the representative on March 16, 201 8 . The letter purports to serve as an “ earnout objection statement ” (as that term is defined in the merger agreement) and claims that for purposes of determining the commercial milestone payment, the C ompany should be including revenues of certain additional items and products that the C ompany has not been including in its earnout reports. The Company has responded to the representative with its own objection to the earnout objection statement and disputes the basis of the representative’s claims.

Revenue

Revenue	3 Months Ended
	Mar. 31, 2018
Revenue [Abstract]
Revenue	8. 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 condensed consolidated financial statements. Revenue is generated primarily from the sale of disposable surgical 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 disposable surgical 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 based on product indication: open-heart ablation, minimally invasive ablation (MIS), appendage management and valve tools. Shipping and handling activities performed after control over products transfers to customers are considered activities to fulfill the promise to transfer the products rather than as separate promises to customers. Products are sold primarily through a direct sales force and through distributors in select international markets. Terms of sale are generally consistent for both end-users and distributors except that payment terms are generally net 30 days for end-users and net 60 days for distributors, with limited exceptions. 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 (i) the determination of the timing of transfer of control of products to customers, (ii) the allocation of transaction price to bundled products, as well as the allocation of certain product revenues between product categories, and (iii) 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. The Company sells certain disposable products in "kits" or "bundles" where the pricing for the kit or bundle is in total rather than by individual component. The Company allocates kit or bundle price to products based on product cost, which approximates allocation based on standalone selling price. Other products for which revenue is allocated include the Company’s multifunctional pens. The Company allocates revenue generated from the sale of multifunctional pens between the open-heart ablation ( 60% ) and MIS ( 40% ) product categories based on historical usage of products in procedures. In addition, the Company allocates shipping and handling revenue among the Company’s product categories based on the periodic percentage of total revenue for each product category. In the normal course of business, the Company does not accept product returns unless a product is defective as manufactured. The Company establishes estimated provisions for returns based on historical experience. The Company does not provide customers with the right to a refund. The Company expects to be entitled to the total consideration for the products ordered by customers as product pricing is fixed according to the terms of customer contracts and payment terms are short. Payment terms fall within the one-year guidance for the practical expedient which allows the Company to forgo adjustment of the promised amount of consideration for the effects of a significant financing component. The Company excludes taxes assessed by governmental authorities on revenue-producing transactions from the measurement of the transaction price. Costs associated with product sales include commissions and royalties. Considering that product sales are performance obligations in contracts that are satisfied at a point in time, commission expense associated with product sales and royalties paid based on sales of certain products is incurred at that point in time rather than over time. Therefore, the Company applies the practical expedient and recognizes commissions and royalties as expense when incurred because the expense is incurred at a point in time and the amortization period is less than one year. Commissions are recorded as selling expense and royalties are recorded as cost of rev enue in the Condensed Consolidated Statements of Operations and Comprehensive Loss . See Note 11 for disaggregated revenue by geographic area and by product category. 

Income Tax Provision

Income Tax Provision	3 Months Ended
	Mar. 31, 2018
Income Tax Provision [Abstract]
Income Tax Provision	9 . INCOME TAX PROVISION The Company files federal, state, and foreign income tax returns in jurisdictions with varying statutes of limitations . The Company uses the asset and liability method to determine its provision for income taxes. The Company’s provision for income taxes in interim periods is computed by applying its estimated annual effective rate against its pre-tax results for the period. N on-recurring items are recorded during the period in which they occur. The effective tax rate for the three months ended March 31, 2018 and 2017 was (0.47%) and (0.23%) . The Tax Cuts and Jobs Act (TCJA) was enacted o n December 22, 2017 . The TCJA reduces the United States federal corporate income tax rate from 35% to 21% . As a result of the Company’s U . S . valuation allowance on its net U . S . deferred tax assets, the TCJA did not have an impact on the effective tax rate for the three months ended March 31, 2018 as compared to March 31, 2017. Also on December 22, 2017, the SEC staff issued Staff Accounting Bulletin No. 118 (SAB 118) to address the application of U.S. GAAP in situations when a registrant does not have the necessary information available, prepared or analyzed in reasonable detail to complete the accounting for certain income tax effects of the TCJA . The Company is applying the guidance in SAB 118 when accounting for the enactment-date effects of the Act. The Company ha s not completed its analysis of the tax effects of enactment of the TCJA as of March 31, 2018, but it has made a reasonable estimate of some of the effects. In other cases, the Company has not been able to make a reasonable estimate and continue s to account for those items under ASC 740, “ Income Taxes, ” and the provisions of the tax laws that were in effect immediately prior to enactment. In all cases, the Company will continue to make and refine its calculations as additional analysis is completed. E stimates may also be affected as the Company gain s a more thorough understanding of the tax law. These changes are not anticipated to be material to income tax expense as a result of the Company’s U . S . valuation allowance position. E stimate s of the effects on deferred tax balances and material provisions of the TCJA are reflected in the financial statements as follows: Deferred tax assets and liabilities : At December 31, 2017, the Company remeasured certain deferred tax assets and liabilities based on the rates at which they are expected to reverse in the future, which is generally 21%. As a result, t he Company reduced its federal deferred tax assets by $29,480 with an offsetting reduction in its valuation allowance at December 31, 2017. In addition, the Company’s state deferred tax assets and corresponding valuation allowance have been adjusted to account for the impact of the federal rate change on state deferred taxes. Upon further analyses of certain aspects of the TCJA and refinement of calculations during the three months ended March 31, 2018, the Company has not adjusted its provisional amount. The Company expects to finalize its remeasurement of deferred tax assets and liabilities as a result of the TCJA when its 2017 U.S. federal income tax return is filed in 2018. Deemed Repatriation Transition Tax : The TCJA provides for a one-time "deemed repatriation" of accumulated foreign earnings for the year ended December 31, 2017. The Company does not anticipate any tax on a deemed repatriation as a result of its foreign deficits. Compensation and Shared-Based Payment Awards: The TCJA modifies the deductibility of certain employees’ compensation and eliminates the exclusion of performance-based compensation under IRC § 162(m), prospectivel y. The TCJA includes a transition rule that permit s the continued in clusion of performance-based compensation paid pursuant to a written, binding contract which was in effect on November 2, 2017, and which was not modified in any material respect on or after such date. The Company has not completed its analysis of all of its relevant equity compensation agreements to determine if the transition rule appl ies and the deferred tax implications of this provision . Corporate Alternative Minimum Tax (AMT): The repeal of corporate AMT provides companies with the ability to obtain refunds of historic AMT credits. The Company realized a deferred tax benefit of $102 for the year ended December 31, 2017 associated with the release of the valuation allowance on its AMT credits. Bonus Depreciation: The TCJA provides for 100 percent bonus depreciation on personal tangible property expenditures beginning September 27, 2017 through 2022. The bonus depreciation percentage is phased down from 100 percent beginning in 2023 through 2026. The Company is continuing to evaluate its bonus depreciation election. The Company has not accrued any interest and penalties. However, if the situation occurs, the Company will recognize interest and penalties within income tax expense in the Condensed Consolidated Statements of Operations and Comprehensive Loss and within the related tax liability in the Condensed Consolidated Balance Sheets. Federal, state and local tax returns of the Company are routinely subject to review by various taxing authorities.

Equity Compensation Plans

Equity Compensation Plans	3 Months Ended
	Mar. 31, 2018
Equity Compensation Plans [Abstract]
Equity Compensation Plans	10 . EQUITY COMPENSATION PLANS The Company has two share-based incentive plans: the 2014 Stock Incentive Plan (2014 Plan) and the 2008 Employee Stock Purchase Plan (ESPP). Stock Incentive Plan Under the 2014 Plan, the Board of Directors may grant incentive stock options to employees and may grant nonstatutory stock options, restricted stock , restricted stock units, performance shares or stock appreciation rights to employees, directors and consultants. The administrator (currently the Compensation Committee of the Board of Directors) has the authority to determine the terms of any awards, including the number of shares subject to each award, the exercisability of the awards and the form of consideration. As of March 31, 2018 , 10,249 shares of common stock had been reserved for issuance under the 2014 Plan , and 562 shares were available for future grants . Effective March 1, 2018, the Compensation Committee of the Board approved the grant o f performance share awards ( 2018 PSAs) to the Company’s named executive officers and certain other employees pursuant to the Company’s 2014 Stock Incentive Plan. The form of award agreement for the 2018 PSAs ( 2018 PSA Grant Form) provides, among other things, that (i) each 2018 PSA that vests represents the right to receive one share of the Company’s common stock; (ii) the 2018 PSAs vest based on the Company achieving specified performance measurements over a performance period of three years, beginning January 1, 2018; (iii) the performance measurements include revenue CAGR as defined in the 2018 PSA Grant Form; (iv) threshold, target and maximum payout opportunities established for the 2018 PSAs will be used to calculate the number of shares that will be issuable when the award vests, which may range from 0% to 200% of the target amount; (v) any 2018 PSAs that are earned are scheduled to vest and be settled in shares of the Company’s common stock at the end of the performance period; and (vi) all or a portion of the 2018 PSAs may vest following a change of control or a termination of service by reason of death or disability (each as described in greater detail in the 2018 PSA Grant Form). With respect to the 2018 PSAs, the number of shares that vest and are issued to the recipient is based upon the Company’s performance as measured against the specified targets at the end of the three-year performance period as determined by the Compensation Committee of the Board. The Company estimates the fair value of the 2018 PSAs based on its closing stock price on the grant date and will adjust compensation expense over the performance period based on its estimate of performance target achievement. Stock o ptions granted under the 2014 Plan prior to 2018 generally expire ten years from the date of grant and generally vest at a rate of 25% on the first anniversary date of the grant and ratably each month thereafter over the following three years. Restricted stock awards granted prior to 2018 generally vest between one and four years from the date of grant . Beginning in 2018, stock options granted generally vest in one -third increments on the first, second and third anniversaries of the grant date, and restricted stock awards granted generally vest on the grant date anniversaries between one and three years from the date of grant. Restricted stock units vest in one -third increments on the first, second and third anniversaries of the grant date. Employee Stock Purchase Plan The ESPP is available to eligible employees as defined in the plan document. Under the ESPP, shares of the Company’s common stock may be purchased at a discount (currently 15% ) of the lesser of the closing price of the Company’s common stock on the first trading day or the last trading day of the offering period. The offering period (currently six months) and the offering price are subject to change. Participants may not purchase more than $25 of the Company’s common stock in a calendar year and may not purchase a value of more than 3 shares during an offering period. On the first day of each year during the term of the ESPP, the number of shares available for sale under the ESPP may be increased by the lesser of (i) two percent ( 2% ) of the Company’s outstanding shares of common stock as of the close of business on the last business day of the prior calendar year, not to exceed 600 shares, or (ii) a lesser amount determined by the Board of Directors. Shares have not been added to the ESPP since 2011. A s of March 31, 2018 , there were 225 shares available for future issuance under the ESPP. The Company is recommending to stockholders at the 2018 annual meeting the approval of the 2018 Employee Stock Purchase Plan covering an additional 500 shares. Expense Information Under FASB ASC 718 The following table summarizes the allocation of share-based compensation expense related to employees, directors and consultants :      Three Months Ended  March 31,  2018 2017  Cost of revenue $ 237 $ 131  Research and development expenses 591 501  Selling, general and administrative expenses 3,062 2,996  Total $ 3,890 $ 3,628

Segment and Geographic Informat

Segment and Geographic Information	3 Months Ended
	Mar. 31, 2018
Segment and Geographic Information [Abstract]
Segment and Geographic Information	1 1 . SEGMENT AND GEOGRAPHIC INFORMATION 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 a ttributed to geographic areas, based on the location of customers , w as as follows:      Three Months Ended  March 31,  2018 2017  United States $ 38,436 $ 33,268  Europe 5,871 5,189  Asia 2,439 2,651  Other international 248 165  Total international 8,558 8,005  Total revenue $ 46,994 $ 41,273  United States revenue by product type was as follows:      Three Months Ended  March 31,  2018 2017  Open-heart ablation $ 17,579 $ 15,705  Minimally invasive ablation 8,613 8,282  Appendage management 11,797 8,702  Total ablation and appendage management 37,989 32,689  Valve tools 447 579  Total United States $ 38,436 $ 33,268  International revenue by product type was as follows:      Three Months Ended  March 31,  2018 2017  Open-heart ablation $ 4,909 $ 4,590  Minimally invasive ablation 1,792 1,958  Appendage management 1,798 1,395  Total ablation and appendage management 8,499 7,943  Valve tools 59 62  Total international $ 8,558 $ 8,005 The Company’s long-lived assets are located primarily in the United States, except for $1,000 as of March 31, 2018 and $957 as of December 31, 201 7 , which are located primarily in Europe.

Description of Business and S17

Description of Business and Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2018
Description of Business and Summary of Significant Accounting Policies [Abstract]
Nature of the Business	Nature of the Business —The “Company” or “AtriCure” consists of AtriCure, Inc. and its wholly-owned subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation. 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.
Basis of Presentation	Basis of Presentation —The accompanying interim financial statements have been prepared in accordance with the rules and regulations of the Securities and Exchange Commission (SEC). The accompanying interim financial statements are unaudited, but in the opinion of the Company’s management, contain all normal, recurring adjustments considered necessary to present fairly the financial position, results of operations and cash flows for the periods presented in conformity with accounting principles generally accepted in the United States of America (GAAP) applicable to interim periods. Certain information and footnote disclosures included in annual financial statements prepared in accordance with GAAP have been omitted or condensed. The Company believes the disclosures herein are adequate to make the information presented not misleading. Results of operations are not necessarily indicative of the results expected for the full year or for any future period. The accompanying Condensed Consolidated Financial Statements should be read in conjunction with the audited financial statements of the Company included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017 filed with the SEC.
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 in the accompanying Condensed Consolidated Financial Statements.
Investments	Investments —The Company invests primarily in U.S. Government agencies and securities, corporate bonds, commercial paper and asset-backed securities and classifies all investments as available-for-sale. Investments with maturities of less than one year are classified as short-term investments. Investments are recorded at fair value, with unrealized gains and losses recorded as accumulated other comprehensive income. Gains and losses are recognized using the specific identification method when securities are sold and are included in interest income or expense in the Condensed Consolidated Statements of Operations and Comprehensive Loss.
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 8 for further discussion on revenue.
Sales Returns and Allowances	Sales Returns and Allowances —The Company maintains a provision for sales returns and allowances for potential returns of defective or damaged products and products shipped in error and invoice adjustments. The Company adjusts the provision quarterly using a combination of specific identification and an estimated general reserve based on historical experience. Increases to the provision result in a reduction of revenue. The provision is included in accrued liabilities in the Condensed Consolidated Balance Sheets.
Allowance for Doubtful Accounts Receivable	Allowance for Doubtful Accounts Receivable —The Company evaluates the collectability of accounts receivable to determine the appropriate allowance for doubtful accounts. In determining the amount of the allowance, the Company considers aging of accounts, historical credit losses, customer-specific information and other relevant factors. Increases to the allowance result in an increase in selling, general and administrative expenses. The Company reviews accounts and adjusts the allowance based on current circumstances and charges off uncollectible receivables against the allowance when all attempts to collect the receivable have failed. The Company’s history of write-offs against the allowance has not been significant.
Inventories	Inventories —Inventories are stated at the lower of cost or net realizable value based on the first-in, first-out cost method (FIFO). The Company’s industry is characterized by rapid product development and frequent new product introductions. Uncertain timing of product approvals, variability in product launch strategies and variation in product use all impact inventory reserves for excess, obsolete and expired products. An estimated inventory reserve for excess, obsolete and expired inventory is recorded quarterly. Increases to inventory reserves result in an increase in cost of revenue. Inventories are written off against the reserve when they are physically disposed. Inventories consist of the following:      March 31, December 31,  2018 2017  Raw materials $ 8,804 $ 7,755  Work in process 1,803 1,299  Finished goods 11,964 13,397  Inventories $ 22,571 $ 22,451 
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. The estimated useful life by major asset category is the following:      Estimated Useful Life  Generators and related equipment 1 - 3 years  Building under capital lease 15 years  Computers, software and office equipment 3 years  Machinery and equipment 3 - 7 years  Furniture and fixtures 3 - 7 years  Leasehold improvements 5 - 15 years  Equipment under capital leases 3 - 5 years 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 radiofrequency (RF) and cryo generators are generally placed with customers that use the Company’s disposable products. The estimated useful lives of generators are based on anticipated usage by customers and may change in future periods with changes in usage or introduction of new technologies. Depreciation related to generators and related equipment, which is recorded in cost of revenue in the Condensed Consolidated Statements of Operations and Comprehensive Loss, was $827 and $916 for the three months ended March 31, 2018 and 2017 . As of March 31, 2018 and December 31, 2017 , the net carrying value of generators and related equipment included in net property and equipment in the Condensed Consolidated Balance Sheets was $4,754 and $4,656 . The Company at least annually reviews property and equipment for impairment using its best estimates based on reasonable and supportable assumptions and 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. Intangible assets include In Process Research and Development (IPR&D), which represents the value of technology acquired in business combinations that has not yet reached technological feasibility. The primary basis for determining technological feasibility is obtaining specific regulatory approval. 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, IPR&D will be amortized over its estimated useful life. If the IPR&D project is abandoned, the IPR&D would be written off. IPR&D represents an estimate of the fair value of the pre-market approval (PMA) that could result from the CONVERGE IDE clinical trial. The Company at least annually reviews intangible assets for impairment using its best estimates based on reasonable and supportable assumptions and projections.
Goodwill	Goodwill— Goodwill represents the excess of purchase price over the fair value of the net assets acquired in business combinations. The Company has historically tested goodwill for impairment annually on November 30, or more often if impairment indicators are present. The Company’s goodwill is accounted for in a single reporting unit representing the Company as a whole.
Other Noncurrent Liabilities	Other Noncurrent Liabilities— Other noncurrent liabilities consist of contingent consideration recorded in business combinations and other contractual obligations. Although the Company expects to settle a portion of the contingent consideration liability in 2018, the balance is included in noncurrent liabilities as such settlement is both required and expected to be made in shares of the Company’s common stock pursuant to the nContact Surgical, Inc. (nContact) merger agreement.
Other Income (Expense)	Other Income (Expense) — Other income (expense) consists primarily 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 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, taxable income in carry-back years 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.
Net Loss Per Share	Net Loss Per Share —As required under GAAP, 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 4,216 and 4,580 stock options, restricted stock shares, restricted stock units and performance award shares as of March 31, 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 Loss and Accumulated Other Comprehensive Income	Comprehensive Loss and Accumulated Other Comprehensive Income —In addition to net losses, the comprehensive loss includes foreign currency translation adjustments and unrealized losses on investments. Accumulated other comprehensive income (loss) consisted of the following (net of tax):      Three Months Ended  March 31,  2018 2017  Total accumulated other comprehensive income (loss) at beginning of period $ 34 $ (468)  Unrealized Losses on Investments  Balance at beginning of period $ (6) $ (21)  Other comprehensive (loss) income before reclassifications (8) 2  Amounts reclassified from accumulated other comprehensive income (loss) to other income (loss) — —  Balance at end of period $ (14) $ (19)  Foreign Currency Translation Adjustment  Balance at beginning of period $ 40 $ (447)  Other comprehensive income before reclassifications 168 52  Amounts reclassified from accumulated other comprehensive income (loss) to other income (loss) (82) 21  Balance at end of period $ 126 $ (374)  Total accumulated other comprehensive income (loss) at end of period $ 112 $ (393) 
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 and regulatory affairs.
Advertising Costs	Advertising Costs — The Company expenses advertising costs as incurred. Advertising costs were not significant during the three months ended March 31, 2018 and 2017 .
Share-Based Compensation	Share-Based Compensation —As required under GAAP, the Company records share-based compensation for all employee share-based payment awards, including stock options, restricted stock, restricted stock units, performance shares and stock purchases related to an employee stock purchase plan, based on estimated fair values. The Company recognized share-based compensation expense of $3,890 and $3,628 for the three months ended March 31, 2018 and 2017 . The fair value of share-based payment awards is estimated on the date of grant using an option-pricing model. The value of the portion of the award that is ultimately expected to vest, net of estimated forfeitures, is recognized as expense over the service periods in the Company’s Condensed Consolidated Statements of Operations and Comprehensive Loss. The Company estimates forfeitures at the time of grant and revises them 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 a number of subjective variables. These variables include, but are not limited to, the Company’s expected stock price volatility over the term of the awards and actual and projected employee stock option exercise behaviors. The fair value of market-based performance option grants is estimated at the date of grant using a Monte-Carlo simulation. The value of the portion of the awards that is ultimately expected to vest is recognized as expense over the service periods in the Condensed Consolidated Statements of Operations and Comprehensive Loss. The Company estimates the fair value of restricted stock, restricted stock units and performance shares based upon the grant date closing market price of the Company’s common stock. The Company also has an employee stock purchase plan (ESPP) which is available to all eligible employees as defined by the plan document. Under the ESPP, shares of the Company’s common stock may be purchased at a discount. The Company estimates the number of shares to be purchased under the ESPP at the beginning of each purchase period based upon the fair value of the stock at the beginning of the purchase period using the Black-Scholes model and records estimated compensation expense during the period. Expense is trued up to actual at the time of stock purchase.
Use of Estimates	 Use of Estimates —The preparation of the financial statements in conformity with 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.

Description of Business and S18

Description of Business and Summary of Significant Accounting Policies (Tables)	3 Months Ended
	Mar. 31, 2018
Description of Business and Summary of Significant Accounting Policies [Abstract]
Summary Of Inventories	Inventories consist of the following:      March 31, December 31,  2018 2017  Raw materials $ 8,804 $ 7,755  Work in process 1,803 1,299  Finished goods 11,964 13,397  Inventories $ 22,571 $ 22,451 
Summary of Property and Equipment	   Estimated Useful Life  Generators and related equipment 1 - 3 years  Building under capital lease 15 years  Computers, software and office equipment 3 years  Machinery and equipment 3 - 7 years  Furniture and fixtures 3 - 7 years  Leasehold improvements 5 - 15 years  Equipment under capital leases 3 - 5 years 
Accumulated Other Comprehensive Income (Loss)	Accumulated other comprehensive income (loss) consisted of the following (net of tax):      Three Months Ended  March 31,  2018 2017  Total accumulated other comprehensive income (loss) at beginning of period $ 34 $ (468)  Unrealized Losses on Investments  Balance at beginning of period $ (6) $ (21)  Other comprehensive (loss) income before reclassifications (8) 2  Amounts reclassified from accumulated other comprehensive income (loss) to other income (loss) — —  Balance at end of period $ (14) $ (19)  Foreign Currency Translation Adjustment  Balance at beginning of period $ 40 $ (447)  Other comprehensive income before reclassifications 168 52  Amounts reclassified from accumulated other comprehensive income (loss) to other income (loss) (82) 21  Balance at end of period $ 126 $ (374)  Total accumulated other comprehensive income (loss) at end of period $ 112 $ (393) 

Fair Value (Tables)

Fair Value (Tables)	3 Months Ended
	Mar. 31, 2018
Fair Value [Abstract]
Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis	The following table represents the Company’s fair value hierarchy for its financial assets and liabilities measured at fair value on a recurring basis as of March 31, 2018 :      Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Other Unobservable Inputs (Level 3) Total  Assets:  Money market funds $ — $ 4,087 $ — $ 4,087  Commercial paper — 11,750 — 11,750  U.S. government agencies and securities 1,250 — — 1,250  Corporate bonds — 5,606 — 5,606  Asset-backed securities — 3,038 — 3,038  Total assets $ 1,250 $ 24,481 $ — $ 25,731  Liabilities:  Acquisition-related contingent consideration — — 37,098 37,098  Total liabilities $ — $ — $ 37,098 $ 37,098 There were no changes in the levels or methodology of measurement of financial assets and liabilities during the three months ended March 31, 2018 . The following table represents the Company’s fair value hierarchy for its financial assets and liabilities measured at fair value on a recurring basis as of December 31, 2017 :      Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Other Unobservable Inputs (Level 3) Total  Assets:  Money market funds $ — $ 12,774 $ — $ 12,774  Commercial paper — 7,472 — 7,472  U.S. government agencies and securities 2,999 — — 2,999  Corporate bonds — 2,920 — 2,920  Total assets $ 2,999 $ 23,166 $ — $ 26,165  Liabilities:  Acquisition-related contingent consideration — — 37,098 37,098  Total liabilities $ — $ — $ 37,098 $ 37,098 
Level 3 Fair Value Measurements Using Significant Other Unobservable Inputs for Acquisition-Related Contingent Consideration	The following table represents the Company’s Level 3 fair value measurements using significant other unobservable inputs for acquisition-related contingent consideration:        Three Months Ended Twelve Months Ended  March 31, 2018 December 31, 2017  Beginning Balance $ 37,098 $ 41,176  Amounts acquired — —  Changes in fair value included in earnings — (4,078)  Ending Balance $ 37,098 $ 37,098 

Intangible Assets (Tables)

Intangible Assets (Tables)	3 Months Ended
	Mar. 31, 2018
Intangible Assets [Abstract]
Company's Intangible Assets	The following table provides a summary of the Company’s intangible assets:      March 31, 2018 December 31, 2017  Estimated Useful Life Cost Accumulated Amortization Cost Accumulated Amortization  Fusion technology 10 years $ 9,242 $ 3,928 $ 9,242 $ 3,697  Clamp & probe technology 3 years 829 829 829 829  SUBTLE access technology 5 years 2,179 1,092 2,179 981  IPR&D 44,021 — 44,021 —  Total $ 56,271 $ 5,849 $ 56,271 $ 5,507 
Future Amortization Expense Related to Intangible Assets with Definite Lives	A mortization expense of intangible assets with definite lives is projected as follows:      2018 $ 1,025 April 1, 2018 through December 31, 2018  2019 1,367  2020 1,235  2021 924  2022 925  2023 and thereafter 925  Total $ 6,401 

Accrued Liabilities (Tables)

Accrued Liabilities (Tables)	3 Months Ended
	Mar. 31, 2018
Accrued Liabilities [Abstract]
Accrued Liabilities	Accrued liabilities consisted of the following:      March 31, December 31,  2018 2017  Accrued payroll and employee-related expenses $ 5,323 $ 4,097  Accrued commissions 4,353 6,964  Accrued bonus 1,987 4,726  Sales returns and allowances 1,174 1,169  Accrued royalties 645 626  Accrued taxes and value-added taxes payable 619 634  Other accrued liabilities 613 695  Total $ 14,714 $ 18,911 

Indebtedness (Tables)

Indebtedness (Tables)	3 Months Ended
	Mar. 31, 2018
Indebtedness [Abstract]
Future Maturities On Debt And Capital Lease Obligations	   2018 $ 1,103 April 1, 2018 through December 31, 2018  2019 5,297  2020 12,936  2021 12,941  2022 12,965  2023 and thereafter 14,173  Total payments $ 59,415  Imputed interest (6,901)  Net long-term debt and capital lease obligations, of which $575 is current and $51,939 is noncurrent $ 52,514 

Equity Compensation Plans (Tabl

Equity Compensation Plans (Tables)	3 Months Ended
	Mar. 31, 2018
Equity Compensation Plans [Abstract]
Share-Based Compensation Expense Related to Employee Share-Based Compensation	The following table summarizes the allocation of share-based compensation expense related to employees, directors and consultants :      Three Months Ended  March 31,  2018 2017  Cost of revenue $ 237 $ 131  Research and development expenses 591 501  Selling, general and administrative expenses 3,062 2,996  Total $ 3,890 $ 3,628 

Segment and Geographic Inform24

Segment and Geographic Information (Tables)	3 Months Ended
	Mar. 31, 2018
Segment and Geographic Information [Abstract]
Revenue by Geographic Area	w as as follows:      Three Months Ended  March 31,  2018 2017  United States $ 38,436 $ 33,268  Europe 5,871 5,189  Asia 2,439 2,651  Other international 248 165  Total international 8,558 8,005  Total revenue $ 46,994 $ 41,273 
Revenue by Product Type	United States revenue by product type was as follows:      Three Months Ended  March 31,  2018 2017  Open-heart ablation $ 17,579 $ 15,705  Minimally invasive ablation 8,613 8,282  Appendage management 11,797 8,702  Total ablation and appendage management 37,989 32,689  Valve tools 447 579  Total United States $ 38,436 $ 33,268  International revenue by product type was as follows:      Three Months Ended  March 31,  2018 2017  Open-heart ablation $ 4,909 $ 4,590  Minimally invasive ablation 1,792 1,958  Appendage management 1,798 1,395  Total ablation and appendage management 8,499 7,943  Valve tools 59 62  Total international $ 8,558 $ 8,005 

Description of Business and S25

Description of Business and Summary of Significant Accounting Policies (Narrative) (Details) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Description Of Business And Significant Accounting Policies [Line Items]
Depreciation	$ 1,857	$ 1,962
Net carrying amount of loaned equipment	$ 28,549		$ 28,749
Options, restricted stock and performance based shares excluded from calculation of net loss per share	4,216	4,580
Share-based compensation expense recognized	$ 3,890	$ 3,628
Generators [Member]
Description Of Business And Significant Accounting Policies [Line Items]
Depreciation	827	$ 916
Carrying Amount of Loaned Equipment [Member]
Description Of Business And Significant Accounting Policies [Line Items]
Net carrying amount of loaned equipment	$ 4,754		$ 4,656
Short-term Debt [Member]
Description Of Business And Significant Accounting Policies [Line Items]
Maturity period of short term investment	1 year

Description of Business and S26

Description of Business and Summary of Significant Accounting Policies (Summary Of Inventories) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Description of Business and Summary of Significant Accounting Policies [Abstract]
Raw materials	$ 8,804	$ 7,755
Work in process	1,803	1,299
Finished goods	11,964	13,397
Inventories	$ 22,571	$ 22,451

Description of Business and S27

Description of Business and Summary of Significant Accounting Policies (Summary Of Property And Equipment) (Details)	3 Months Ended
	Mar. 31, 2018
Building under Capital Lease [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	15 years
Computers, Software and Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	3 years
Minimum [Member] | Generator and Related Equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	1 year
Minimum [Member] | Machinery And Equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	3 years
Minimum [Member] | Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	3 years
Minimum [Member] | Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	5 years
Minimum [Member] | Equipment under Capital Leases [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	3 years
Maximum [Member] | Generator and Related Equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	3 years
Maximum [Member] | Machinery And Equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	7 years
Maximum [Member] | Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	7 years
Maximum [Member] | Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	15 years
Maximum [Member] | Equipment under Capital Leases [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	5 years

Description of Business and S28

Description of Business and Summary of Significant Accounting Policies (Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total accumulated other comprehensive income (loss) at beginning of period	$ 34	$ (468)
Total accumulated other comprehensive income (loss) at end of period	112	(393)
Unrealized Losses On Investments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total accumulated other comprehensive income (loss) at beginning of period	(6)	(21)
Other comprehensive (loss) income before reclassifications	(8)	2
Amounts reclassified from accumulated other comprehensive income (loss) to other income (loss)
Total accumulated other comprehensive income (loss) at end of period	(14)	(19)
Foreign Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total accumulated other comprehensive income (loss) at beginning of period	40	(447)
Other comprehensive (loss) income before reclassifications	168	52
Amounts reclassified from accumulated other comprehensive income (loss) to other income (loss)	(82)	21
Total accumulated other comprehensive income (loss) at end of period	$ 126	$ (374)

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	Mar. 31, 2018	Dec. 31, 2017
Assets:
Total assets	$ 25,731	$ 26,165
Liabilities:
Acquisition-related contingent consideration	37,098	37,098
Total liabilities	37,098	37,098
Money Market Funds [Member]
Assets:
Total assets	4,087	12,774
Commercial Paper [Member]
Assets:
Total assets	11,750	7,472
U.S. Government Agencies and Securities [Member]
Assets:
Total assets	1,250	2,999
Corporate Bonds [Member]
Assets:
Total assets	5,606	2,920
Asset-backed Securities [Member]
Assets:
Total assets	3,038
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets:
Total assets	1,250	2,999
Liabilities:
Acquisition-related contingent consideration
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | U.S. Government Agencies and Securities [Member]
Assets:
Total assets	1,250	2,999
Significant Other Observable Inputs (Level 2) [Member]
Assets:
Total assets	24,481	23,166
Liabilities:
Acquisition-related contingent consideration
Significant Other Observable Inputs (Level 2) [Member] | Money Market Funds [Member]
Assets:
Total assets	4,087	12,774
Significant Other Observable Inputs (Level 2) [Member] | Commercial Paper [Member]
Assets:
Total assets	11,750	7,472
Significant Other Observable Inputs (Level 2) [Member] | Corporate Bonds [Member]
Assets:
Total assets	5,606	2,920
Significant Other Observable Inputs (Level 2) [Member] | Asset-backed Securities [Member]
Assets:
Total assets	3,038
Significant Other Unobservable Inputs (Level 3) [Member]
Liabilities:
Acquisition-related contingent consideration	37,098	37,098
Total liabilities	$ 37,098	$ 37,098

Fair Value (Level 3 Fair Value

Fair Value (Level 3 Fair Value Measurements Using Significant Other Unobservable Inputs for Acquisition-Related Contingent Consideration) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Fair Value [Abstract]
Beginning Balance	$ 37,098	$ 41,176
Amounts acquired
Changes in fair value included in earnings		(4,078)
Ending Balance	$ 37,098	$ 37,098

Intangible Assets (Narative) (D

Intangible Assets (Narative) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Intangible Assets [Abstract]
Amortization of intangible assets	$ 342	$ 342

Intangible Assets (Company's In

Intangible Assets (Company's Intangible Assets) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Cost	$ 56,271	$ 56,271
Accumulated Amortization	$ 5,849	5,507
Fusion Technology [Member]
Finite-Lived Intangible Assets [Line Items]
Estimated Useful Life	10 years
Cost	$ 9,242	9,242
Accumulated Amortization	$ 3,928	3,697
Clamp and Probe Technology [Member]
Finite-Lived Intangible Assets [Line Items]
Estimated Useful Life	3 years
Cost	$ 829	829
Accumulated Amortization	$ 829	829
SUBTLE Access Technology [Member]
Finite-Lived Intangible Assets [Line Items]
Estimated Useful Life	5 years
Cost	$ 2,179	2,179
Accumulated Amortization	1,092	981
IPR&D [Member]
Finite-Lived Intangible Assets [Line Items]
Cost	$ 44,021	$ 44,021

Intangible Assets (Future Amort

Intangible Assets (Future Amortization Expense Related to Intangible Assets with Definite Lives) (Details) $ in Thousands	Mar. 31, 2018USD ($)
Intangible Assets [Abstract]
2,018	$ 1,025
2,019	1,367
2,020	1,235
2,021	924
2,022	925
2023 and thereafter	925
Total	$ 6,401

Accrued Liabilities (Accrued Li

Accrued Liabilities (Accrued Liabilities) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Accrued Liabilities [Abstract]
Accrued payroll and employee-related expenses	$ 5,323	$ 4,097
Accrued commissions	4,353	6,964
Accrued bonus	1,987	4,726
Sales returns and allowances	1,174	1,169
Accrued royalties	645	626
Accrued taxes and value-added taxes payable	619	634
Other accrued liabilities	613	695
Total	$ 14,714	$ 18,911

Indebtedness (Narrative) (Detai

Indebtedness (Narrative) (Details) - USD ($)	Feb. 23, 2018	Apr. 25, 2016	Mar. 31, 2018	Oct. 31, 2015
Line of Credit Facility [Line Items]
Accumulated amortization on the capital leases			$ 2,478,000
Maximum [Member]
Line of Credit Facility [Line Items]
Letter of credit required to landlord			1,250,000
Silicon Valley Bank Agreement [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of credit			0
Line of credit, availability			$ 18,750,000
Silicon Valley Bank, Second Amended And Restated Loan Agreement [Member]
Line of Credit Facility [Line Items]
Principal payment starting period after inception of loan to maturity		18 months
Silicon Valley Bank, Amended And Restated Loan Agreement Effective 2/23/18 [Member]
Line of Credit Facility [Line Items]
Upon certain conditions met, deferred loan payment period			6 months
Silicon Valley Bank, Amended And Restated Loan Agreement Effective 2/23/18 [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of credit, maximum borrowing capacity	$ 20,000,000
Maturity date			Apr. 30, 2021
Optional increase in line of credit	$ 20,000,000
Additional fee on total term loan			0.33%
Silicon Valley Bank, Amended And Restated Loan Agreement Effective 2/23/18 [Member] | Revolving Credit Facility [Member] | Prime Rate [Member]
Line of Credit Facility [Line Items]
Basis rate			4.50%
Building And Computer Equipment [Member]
Line of Credit Facility [Line Items]
Capital lease expiration period			Dec. 31, 2030
Cost of assets under lease			$ 14,472,000
Term Loan [Member] | Silicon Valley Bank, Second Amended And Restated Loan Agreement [Member]
Line of Credit Facility [Line Items]
Loan term	5 years
Term Loan [Member] | Silicon Valley Bank, Amended And Restated Loan Agreement Effective 2/23/18 [Member]
Line of Credit Facility [Line Items]
Loan amount	$ 40,000,000
Additional fee on total term loan		3.50%
Accrued fee amount			23,000
Financing costs			$ 722,000
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			3.75%
Interest rate			8.25%
Mason Lease [Member] | Letter of Credit [Member]
Line of Credit Facility [Line Items]
Letter of credit outstanding				$ 1,250,000

Indebtedness (Future Maturities

Indebtedness (Future Maturities On Debt And Capital Lease Obligations) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Indebtedness [Abstract]
2,018	$ 1,103
2,019	5,297
2,020	12,936
2,021	12,941
2,022	12,965
2023 and thereafter	14,173
Total payments	59,415
Imputed interest	(6,901)
Net long-term debt and capital lease obligations, of which $575 is current and $51,939 is noncurrent	52,514
Net capital lease obligations, current	575	$ 561
Net capital lease obligations, noncurrent	$ 51,939

Commitments and Contingencies (

Commitments and Contingencies (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Commitments and Contingencies [Line Items]
Royalty expense	$ 672	$ 534
Minimum [Member]
Commitments and Contingencies [Line Items]
Royalty rates	3.00%
Royalty agreement term	18 years
Maximum [Member]
Commitments and Contingencies [Line Items]
Royalty rates	5.00%
Royalty agreement term	20 years
Office, Manufacturing, Warehouse Facilities, And Equipment [Member]
Commitments and Contingencies [Line Items]
Operating leases expire at various terms	Dec. 31, 2022

Revenue (Narrative) (Details)

Revenue (Narrative) (Details)	3 Months Ended
	Mar. 31, 2018
Open-heart Ablation [Member]
Disaggregation of Revenue [Line Items]
Revenue allocation percentage	60.00%
Minimally Invasive Ablation [Member]
Disaggregation of Revenue [Line Items]
Revenue allocation percentage	40.00%

Income Tax Provision (Narrative

Income Tax Provision (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Income Tax Provision [Abstract]
Effective tax rate	(0.47%)	(0.23%)
Federal tax at statutory rate	21.00%		35.00%
Reduction to federal deferred tax assets			$ 29,480
Corporate alternative minimum tax, deferred tax benefit			$ 102

Equity Compensation Plans (Narr

Equity Compensation Plans (Narrative) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018USD ($)itemshares	Mar. 31, 2017USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of share-based incentive plans | item	2
Share-based compensation expense recognized | $	$ 3,890	$ 3,628
Share-based compensation expense | $	$ 3,890	$ 3,628
Participants purchase limit shares	3,000
Offering period	6 months
Minimum [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	1 year
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]
Expiry of options from the date of grant	10 years
Common stock reserved for issuance	10,249,000
Shares available for future grants	562,000
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]
Common stock reserved for issuance	225,000
Company's common stock may be purchased at a discount	15.00%
Participants purchase limit value | $	$ 25
Shares available for sale under the ESPP increased	2.00%
Outstanding shares of common stock exceed	600,000
2018 PSAs [Member] | Performance Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting right of shares of common stock	1
Vesting period	3 years
2018 PSAs [Member] | Minimum [Member] | Performance Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance stock award threshold, target and maximum payout opportunity percentage	0.00%
2018 PSAs [Member] | Maximum [Member] | Performance Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance stock award threshold, target and maximum payout opportunity percentage	200.00%
2018 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance	500,000
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] | Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual vesting percentage	0.33%
First, Second, And Third Anniversaries [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual vesting percentage	0.33%

Equity Compensation Plans (Shar

Equity Compensation Plans (Share-Based Compensation Expense Related to Employee Share-Based Compensation) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total	$ 3,890	$ 3,628
Cost of Revenue [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total	237	131
Research and Development Expenses [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total	591	501
Selling, General and Administrative Expenses [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total	$ 3,062	$ 2,996

Segment and Geographic Inform42

Segment and Geographic Information (Narrative)(Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Netherlands [Member]
Long-lived assets	$ 1,000	$ 957

Segment and Geographic Inform43

Segment and Geographic Information (Revenue by Geographic Area) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	$ 46,994	$ 41,273
United States [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	38,436	33,268
Europe [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	5,871	5,189
Asia [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	2,439	2,651
Other International [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	248	165
International [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	$ 8,558	$ 8,005

Segment and Geographic Inform44

Segment and Geographic Information (Revenue by Product Type) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenue from External Customer [Line Items]
Revenue	$ 46,994	$ 41,273
United States [Member]
Revenue from External Customer [Line Items]
Revenue	38,436	33,268
United States [Member] | Open-heart Ablation [Member]
Revenue from External Customer [Line Items]
Revenue	17,579	15,705
United States [Member] | Minimally Invasive Ablation [Member]
Revenue from External Customer [Line Items]
Revenue	8,613	8,282
United States [Member] | Appendage Management [Member]
Revenue from External Customer [Line Items]
Revenue	11,797	8,702
United States [Member] | Ablation And Appendage Management [Member]
Revenue from External Customer [Line Items]
Revenue	37,989	32,689
United States [Member] | Valve Tools [Member]
Revenue from External Customer [Line Items]
Revenue	447	579
International [Member]
Revenue from External Customer [Line Items]
Revenue	8,558	8,005
International [Member] | Open-heart Ablation [Member]
Revenue from External Customer [Line Items]
Revenue	4,909	4,590
International [Member] | Minimally Invasive Ablation [Member]
Revenue from External Customer [Line Items]
Revenue	1,792	1,958
International [Member] | Appendage Management [Member]
Revenue from External Customer [Line Items]
Revenue	1,798	1,395
International [Member] | Ablation And Appendage Management [Member]
Revenue from External Customer [Line Items]
Revenue	8,499	7,943
International [Member] | Valve Tools [Member]
Revenue from External Customer [Line Items]
Revenue	$ 59	$ 62