Abiomed (ABMD) 10-K 24 May 18 2018 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Mar. 31, 2018	May 08, 2018	Sep. 30, 2017
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Mar. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	FY
Trading Symbol	ABMD
Entity Registrant Name	ABIOMED INC
Entity Central Index Key	815,094
Current Fiscal Year End Date	--03-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		44,477,837
Entity Public Float			$ 7,452,252,182

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2018	Mar. 31, 2017
Current assets:
Cash and cash equivalents	$ 42,975	$ 39,040
Short-term marketable securities	319,274	190,908
Accounts receivable, net	70,010	54,055
Inventories	50,204	34,931
Prepaid expenses and other current assets	11,808	8,024
Total current assets	494,271	326,958
Long-term marketable securities	37,502	47,143
Property and equipment, net	117,167	87,777
Goodwill	35,808	31,045
In-process research and development	16,705	14,482
Long-term deferred tax assets, net	70,746	34,723
Other assets	14,176	8,286
Total assets	786,375	550,414
Current liabilities:
Accounts payable	23,565	20,620
Accrued expenses and other liabilities	46,147	37,703
Deferred revenue	14,970	10,495
Current portion of capital lease obligation		799
Total current liabilities	84,682	69,617
Other long-term liabilities	776	3,251
Contingent consideration	10,490	9,153
Long-term deferred tax liabilities	903	783
Capital lease obligation, net of current portion		15,539
Total liabilities	96,851	98,343
Commitments and contingencies (Note 11)
Stockholders' equity:
Class B Preferred Stock, $.01 par value Authorized - 1,000,000 shares; Issued and outstanding - none
Common stock, $.01 par value Authorized - 100,000,000 shares; Issued - 46,100,649 shares at March 31, 2018 and 45,249,281 shares at March 31, 2017; Outstanding - 44,375,337 shares at March 31, 2018 and 43,673,286 shares at March 31, 2017	444	437
Additional paid in capital	619,905	565,962
Retained earnings (Accumulated deficit)	140,457	(46,959)
Treasury stock at cost - 1,725,312 shares at March 31, 2018 and 1,575,995 shares at March 31, 2017	(67,078)	(46,763)
Accumulated other comprehensive loss	(4,204)	(20,606)
Total stockholders' equity	689,524	452,071
Total liabilities and stockholders' equity	$ 786,375	$ 550,414

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2018	Mar. 31, 2017
Statement Of Financial Position [Abstract]
Class B Preferred Stock, par value	$ 0.01	$ 0.01
Class B Preferred Stock, Authorized	1,000,000	1,000,000
Class B Preferred Stock, Issued	0	0
Class B Preferred Stock, outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, Authorized	100,000,000	100,000,000
Common stock, Issued	46,100,649	45,249,281
Common stock, Outstanding	44,375,337	43,673,286
Treasury stock, shares	1,725,312	1,575,995

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Mar. 31, 2018		Mar. 31, 2017	Mar. 31, 2016
Income Statement [Abstract]
Revenue	$ 593,749		$ 445,304	$ 329,543
Costs and expenses:
Cost of revenue	98,581		70,627	50,419
Research and development	75,297		66,386	49,759
Selling, general and administrative	262,734		218,153	164,261
Costs and Expenses, Total	436,612		355,166	264,439
Income from operations	157,137		90,138	65,104
Other income:
Investment income, net	3,688		1,554	395
Other (expense) income, net	(388)		(349)	339
Nonoperating Income (Expense), Total	3,300		1,205	734
Income before income taxes	160,437		91,343	65,838
Income tax provision	48,267	[1],[2]	39,227	27,691
Net income	$ 112,170		$ 52,116	$ 38,147
Basic net income per share	$ 2.54		$ 1.21	$ 0.90
Basic weighted average shares outstanding	44,153		43,238	42,204
Diluted net income per share	$ 2.45		$ 1.17	$ 0.85
Diluted weighted average shares outstanding	45,849		44,658	44,895
[1]	In the first quarter of fiscal 2018, the Company adopted Accounting Standards Update No. 2016-09, Improvements to Employee Share-Based Payment Accounting, which requires that all excess tax benefits and tax deficiencies related share-based compensation arrangements be recognized as income tax benefit or expense, instead of in stockholders’ equity as previous guidance required. The income tax benefit for the year ended March 31, 2018 included excess tax benefits of $31.0 million. These recognized excess tax benefits resulted from restricted stock units that vested or stock options that were exercised during the year ended March 31, 2018.
[2]	On December 22, 2017, the Tax Cuts and Jobs Act, or Tax Reform Act, was enacted into law. This new law, among other items, reduces the U.S. federal statutory corporate income tax rate from 35% to 21% effective January 1, 2018. During the year ended March 31, 2018, the Company recorded tax expense adjustments for $21.4 million related to the revaluation of its deferred taxes due to a reduction of the U.S. federal statutory corporate income tax rate.

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 112,170	$ 52,116	$ 38,147
Other comprehensive income (loss):
Foreign currency translation gains (losses)	16,862	(5,855)	2,724
Net unrealized (losses) gain on marketable securities	(460)	(211)	66
Other comprehensive income (loss)	16,402	(6,066)	2,790
Comprehensive income	$ 128,572	$ 46,050	$ 40,937

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Treasury Stock	Additional Paid in Capital	Retained Earnings (Accumulated Deficit)	Accumulated Other Comprehensive Income (Loss)
Beginning Balance at Mar. 31, 2015	$ 291,560	$ 413	$ (19,347)	$ 465,046	$ (137,222)	$ (17,330)
Beginning Balance (in shares) at Mar. 31, 2015		41,335,773	1,282,944
Restricted stock units issued		$ 5		(5)
Restricted stock units issued (in shares)		507,471
Stock options exercised	9,771	$ 8		9,763
Stock options exercised (in shares)		829,385
Stock issued under employee stock purchase plan	1,135			1,135
Stock issued under employee stock purchase plan (in shares)		16,772
Stock issued to directors	65			65
Stock issued to directors (in shares)		774
Return of common stock to pay withholding taxes on restricted stock	(7,313)		$ (7,313)
Return of common stock to pay withholding taxes on restricted stock (in shares)		(93,947)	93,947
Stock compensation expense	29,053			29,053
Excess tax benefit from stock-based awards	3,567			3,567
Other comprehensive income (loss)	2,790					2,790
Net income	38,147				38,147
Ending Balance at Mar. 31, 2016	368,775	$ 426	$ (26,660)	508,624	(99,075)	(14,540)
Ending Balance (in shares) at Mar. 31, 2016		42,596,228	1,376,891
Restricted stock units issued		$ 5		(5)
Restricted stock units issued (in shares)		502,417
Stock options exercised	10,660	$ 8		10,652
Stock options exercised (in shares)		754,893
Stock issued under employee stock purchase plan	1,720			1,720
Stock issued under employee stock purchase plan (in shares)		18,288
Stock issued to directors	67			67
Stock issued to directors (in shares)		564
Return of common stock to pay withholding taxes on restricted stock	(20,105)	$ (2)	$ (20,103)
Return of common stock to pay withholding taxes on restricted stock (in shares)		(199,104)	199,104
Stock compensation expense	32,866			32,866
Excess tax benefit from stock-based awards	12,038			12,038
Other comprehensive income (loss)	(6,066)					(6,066)
Net income	52,116				52,116
Ending Balance at Mar. 31, 2017	$ 452,071	$ 437	$ (46,763)	565,962	(46,959)	(20,606)
Ending Balance (in shares) at Mar. 31, 2017	43,673,286	43,673,286	1,575,995
Cumulative effect of adoption of new accounting standard	$ 77,081			1,835	75,246
Restricted stock units issued		$ 4		(4)
Restricted stock units issued (in shares)		371,940
Stock options exercised	$ 9,303	$ 5		9,298
Stock options exercised (in shares)	460,000	459,777
Stock issued under employee stock purchase plan	$ 2,394			2,394
Stock issued under employee stock purchase plan (in shares)		19,286
Stock issued to directors	67			67
Stock issued to directors (in shares)		365
Return of common stock to pay withholding taxes on restricted stock	(20,317)	$ (2)	$ (20,315)
Return of common stock to pay withholding taxes on restricted stock (in shares)		(149,317)	149,317
Stock compensation expense	40,353			40,353
Other comprehensive income (loss)	16,402					16,402
Net income	112,170				112,170
Ending Balance at Mar. 31, 2018	$ 689,524	$ 444	$ (67,078)	$ 619,905	$ 140,457	$ (4,204)
Ending Balance (in shares) at Mar. 31, 2018	44,375,337	44,375,337	1,725,312

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Operating activities:
Net income	$ 112,170	$ 52,116	$ 38,147
Adjustments required to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	11,005	6,202	3,277
Bad debt expense	38	159	42
Stock-based compensation	40,353	32,866	29,053
Write-down of inventory and other	3,946	3,085	2,094
Excess tax benefit from stock-based awards		(12,038)	(3,567)
Deferred tax provision	42,624	25,803	22,296
Change in fair value of contingent consideration	1,337	1,590	1,053
Changes in assets and liabilities:
Accounts receivable	(15,289)	(11,550)	(10,930)
Inventories	(15,686)	(12,284)	(11,473)
Prepaid expenses and other assets	(4,466)	(2,366)	(2,290)
Accounts payable	4,412	7,565	(2,645)
Accrued expenses and other liabilities	7,722	22,223	10,020
Deferred revenue	4,380	1,745	1,718
Net cash provided by operating activities	192,546	115,116	76,795
Investing activities:
Purchases of marketable securities	(325,408)	(278,501)	(260,975)
Proceeds from the sale and maturity of marketable securities	206,909	205,482	219,639
Purchase of other investment	(6,400)	(2,899)	(750)
Purchases of property and equipment	(55,863)	(50,415)	(15,624)
Net cash used for investing activities	(180,762)	(126,333)	(57,710)
Financing activities:
Proceeds from the exercise of stock options	9,303	10,660	9,771
Excess tax benefit from stock-based awards		12,038	3,567
Taxes paid related to net share settlement upon vesting of stock awards	(20,317)	(20,105)	(7,313)
Proceeds from the issuance of stock under employee stock purchase plan	2,394	1,720	1,135
Principal payments on capital lease obligation	(517)	(446)
Net cash (used for) provided by financing activities	(9,137)	3,867	7,160
Effect of exchange rate changes on cash	1,288	(1,841)	(415)
Net increase in cash and cash equivalents	3,935	(9,191)	25,830
Cash and cash equivalents at beginning of year	39,040	48,231	22,401
Cash and cash equivalents at end of year	42,975	39,040	48,231
Supplemental disclosure of cash flow information:
Cash paid for income taxes	4,641	1,405	848
Cash paid for interest on capital lease obligation	302	354
Supplemental disclosure of non-cash investing and financing activities:
Property and equipment under capital lease obligation		16,784
Property and equipment in accounts payable and accrued expenses	$ 3,338	$ 5,692	$ 1,797

Nature of Operations

Nature of Operations	12 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
Nature of Operations	Note 1. Nature of Operations ABIOMED, Inc. (the “Company” or “Abiomed”) is a provider of mechanical circulatory support devices and offers a continuum of care to heart failure patients. The Company develops, manufactures and markets proprietary products that are designed to enable the heart to rest, heal and recover by improving blood flow and/or performing the pumping function of the heart. The Company’s products are used in the cardiac catheterization lab, or cath lab, by interventional cardiologists and in the heart surgery suite by heart surgeons for patients who are in need of hemodynamic support prophylactically or emergently before, during or after angioplasty or heart surgery procedures.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Note 2. Summary of Significant Accounting Policies The accompanying consolidated financial statements reflect the application of significant accounting policies described below. Principles of Consolidation The accompanying consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation. Use of Estimates The preparation of financial statements in conformity with generally accepted accounting principles of the United States of America, or 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 expenses during the reporting period. The Company bases its estimates on historical experience and various other factors believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying value of assets and liabilities that are not readily apparent from other sources. On an ongoing basis, the Company evaluates its estimates, including those related to revenue recognition, collectability of receivables, realizability of inventory, property and equipment, goodwill, intangible and other long-lived assets, accrued expenses, stock-based compensation, income taxes including deferred tax assets and liabilities, contingencies and litigation. Provisions for depreciation are based on their estimated useful lives using the straight-line method. Some of these estimates can be subjective and complex and, consequently, actual results may differ from these estimates under different assumptions or conditions. Cash Equivalents and Marketable Securities The Company classifies any marketable security with a maturity date of 90 days or less at the time of purchase as a cash equivalent. Cash equivalents are carried on the balance sheet at fair market value. The Company classifies any marketable security with a maturity date of greater than 90 days at the time of purchase as marketable securities and classifies marketable securities with a maturity date of greater than one year from the balance sheet date as long-term marketable securities. Marketable securities that the Company has the positive intent and ability to hold to maturity are reported at amortized cost and classified as held-to-maturity marketable securities. If the Company does not have the intent and ability to hold a marketable security to maturity, it reports the investment as available-for-sale marketable securities. The Company reports available-for-sale marketable securities at fair value, and includes unrealized gains and, to the extent deemed temporary, unrealized losses in stockholders’ equity. If any adjustment to fair value reflects a decline in the value of the investment, the Company considers available evidence to evaluate whether the decline is “other than temporary” and, if so, marks the marketable security to market through a charge reflected on the consolidated statements of operations. Major Customers and Concentrations of Credit Risk The Company primarily sells its products to hospitals and distributors. No customer accounted for more than 10% of total revenues in fiscal years ended March 31, 2018, 2017 or 2016. No individual customer had an accounts receivable balance greater than 10% of total accounts receivable at March 31, 2018 and 2017. Credit is extended based on an evaluation of a customer’s historical financial condition and generally collateral is not required. The Company’s history of credit losses has not been significant and the Company maintains an allowance for doubtful accounts based on its assessment of the collectability of accounts receivable. Accounts receivables are geographically dispersed, primarily throughout the U.S., as well as in Europe and other foreign countries where formal distributor agreements exist in certain countries. Financial instruments which potentially subject the Company to a concentration of credit risk consist of cash, cash equivalents, marketable securities, short and long-term marketable securities and accounts receivable. Management mitigates credit risk by limiting the investment type and maturity to securities that preserve capital, maintain liquidity and have a high credit quality. Financial Instruments The Company’s financial instruments are comprised of cash and cash equivalents, marketable securities, accounts receivable, accounts payable and contingent consideration. The carrying amounts of accounts receivable and accounts payable are considered reasonable estimates of their fair value, due to the short maturity of these investments. Inventories Inventories are stated at the lower of cost or market. Cost is based on the first in, first out method. The Company regularly reviews inventory quantities on hand and writes down to its net realizable value any inventory that it believes to be impaired. Management considers forecast demand in relation to the inventory on hand, competitiveness of product offerings, market conditions and product life cycles when determining excess and obsolescence and net realizable value adjustments. Once inventory is written down and a new cost basis is established, it is not written back up if demand increases. Property and Equipment Property and equipment is recorded at cost less accumulated depreciation. Land is carried at cost and is not depreciated. Depreciation is computed using the straight line method based on estimated useful lives of three to five years for machinery and equipment, computer software, and furniture and fixtures. Building and building improvements are depreciated using the straight-line method over estimated useful lives of seven to thirty-three years. Leasehold improvements are amortized using the straight-line method over the shorter of the lease term or the estimated useful lives of the related assets. Expenditures for maintenance and repairs are expensed as incurred. Upon retirement or other disposition of assets, the costs and related accumulated depreciation are eliminated from the accounts and the resulting gain or loss is reflected in operating expenses. Property and equipment is reviewed for impairment losses whenever events or changes in circumstances indicate the carrying amount may not be recoverable. An impairment loss would be recognized based on the amount by which the carrying value of the asset or asset group exceeds its fair value. Fair value is determined primarily using the estimated future cash flows associated with the asset or asset group under review discounted at a rate commensurate with the risk involved and other valuation techniques. Leases Lease agreements are evaluated to determine whether they are capital or operating leases in accordance with Financial Accounting Standards Board, or ASC, 840, Leases Rent expense for operating leases, which may include free rent or fixed escalation amounts in addition to minimum lease payments, is recognized on a straight-line basis over the duration of each lease term. Goodwill Goodwill is recorded when consideration for an acquisition exceeds the fair value of the net tangible and intangible assets acquired. Goodwill is not amortized, instead the Company evaluates goodwill for impairment at least annually at October 31, as well as whenever events or changes in circumstances suggest that the carrying amount may not be recoverable. Goodwill impairment assessments are performed at the reporting unit level. The goodwill test involves a two-step process. The first step is a comparison of the reporting unit’s fair value to its carrying value. If the reporting unit’s fair value exceeds its carrying value, no further procedures are required. However, if the reporting unit’s fair value is less than the carrying value, an impairment of goodwill may exist, requiring a second step to measure the amount of impairment loss. If the implied fair value of goodwill is less than the recorded goodwill, an impairment charge is recorded for the difference. In applying the goodwill impairment test, the Company may assess qualitative factors to determine whether it is more likely than not that the fair value of the reporting unit is less than its carrying value. Qualitative factors may include, but are not limited to, macroeconomic conditions, industry conditions, the competitive environment, changes in the market for our products and services, regulatory and political developments, cost factors, and entity specific factors such as strategies and overall financial performance. If, after assessing these qualitative factors, the Company determines it is not more likely than not that the fair value of a reporting unit is less than its carrying value, then performing the two-step impairment test is unnecessary. The goodwill impairment test is performed at the reporting unit level by comparing the reporting unit’s carrying value, including goodwill, to the fair value of the reporting unit. The Company estimates the fair value of its single reporting unit using a combination of the income approach and the market approach. The income approach incorporates the use of a discounted cash flow method in which the estimated future cash flows and terminal values for the reporting unit is discounted to a present value using an appropriate discount rate. Cash flow projections are based on management’s estimates of economic and market conditions which drive key assumptions of revenue growth rates, operating margins, cash flows, capital expenditures and working capital requirements. The discount rate is based on the specific risk characteristics of the reporting unit and its underlying forecast. The market approach estimates fair value by comparing publicly traded companies with similar operating and investment characteristics as the reporting unit. The fair values determined by the market approach and income approach, are weighted to determine the fair value for the reporting unit based primarily on the similarity of the operating and investment characteristics of the reporting unit to the comparable publicly traded companies used in the market approach. In-Process Research and Development In-process research and development, or IPR&D, assets are considered to be indefinite-lived until the completion or abandonment of the associated research and development projects. IPR&D assets represent the fair value assigned to technologies that are acquired, which at the time of acquisition have not reached technological feasibility and have no alternative future use. During the period that the IPR&D assets are considered indefinite-lived, they are tested for impairment on an annual basis on October 31, or more frequently if the Company becomes aware of any events occurring or changes in circumstances that indicate that the fair value of the IPR&D assets are less than their carrying values. If and when development is complete, which generally occurs upon regulatory approval and the Company is able to commercialize products associated with the IPR&D assets, these assets are then deemed definite-lived and are amortized based on their estimated useful lives at that point in time. If development is terminated or abandoned, the Company may have a full or partial impairment charge related to the IPR&D assets, calculated as the excess of carrying value of the IPR&D assets over fair value. Contingent Consideration Contingent consideration represents potential milestones that the Company could pay additional consideration for a business acquisition and is recorded as a liability and is measured at fair value using a combination of 1) an income approach, based on various revenue and cost assumptions and applying a probability to each outcome and 2) a Monte-Carlo valuation model that simulates outcomes based on management estimates. With the income approach, p robabilities were applied to each potential scenario and the resulting values were discounted using a rate that considers the weighted average cost of capital, the related projections, and the overall business. The Monte-Carlo valuation model simulates estimated future revenues during the earn out-period using management's best estimates. Accrued Expenses As part of the process of preparing its financial statements, the Company is required to estimate accrued expenses. This process includes identifying services that third parties have performed and estimating the level of service performed and the associated cost incurred on these services as of each balance sheet date in its financial statements. Examples of estimated accrued expenses include contract service fees, such as amounts due to clinical research organizations, investigators in conjunction with clinical trials, professional service fees, such as attorneys and accountants, and third party expenses relating to marketing efforts associated with commercialization of the Company’s product and product candidates. Accrued expenses also include estimates for payroll costs, such as bonuses and commissions. In the event that the Company does not identify certain costs that have been incurred or it under or over-estimates the level of services or the costs of such services, reported expenses for a reporting period could be overstated or understated. The dates in which certain services commence and end, the level of services performed on or before a given date and the cost of services is often subject to the Company’s judgment. The Company makes these judgments and estimates based upon known facts and circumstances. Revenue Recognition The Company recognizes revenue when evidence of an arrangement exists, title has passed or services have been rendered, the selling price is fixed or determinable and collectability is reasonably assured. Revenue from product sales to customers is recognized when delivery has occurred. All costs related to product sales are recognized at time of delivery. The Company does not provide for rights of return to customers on product sales and therefore does not record a provision for returns. Maintenance and service support contract revenues are included in revenue and are recognized ratably over the term of the service contracts. Revenue is recognized as earned in limited instances where the Company rents its console medical devices on a month-to-month basis or for a longer specified period of time to customers. In May 2014, the FASB, issued ASU 2014-09, Revenue from Contracts with Customers to provide updated guidance on revenue recognition. This new standard will replace most of the existing revenue recognition guidance in U.S. GAAP when it becomes effective and permits the use of either the retrospective or cumulative effect transition method. ASU 2014-09 requires a company to recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods or services. In doing so, companies may need to use more judgment and make more estimates than under the current accounting guidance. These may include identifying performance obligations in the contract, estimating the amount of variable consideration to include in the transaction price and allocating the transaction price to each separate performance obligation. The guidance also requires expanded disclosures relating to the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. Additionally, qualitative and quantitative disclosures are required about customer contracts, significant judgments and changes in judgments, and assets recognized from the costs to obtain or fulfill a contract. The Company is implementing the necessary changes to its revenue recognition accounting policies and controls to support recognition and disclosure under the new standard. The Company will adopt ASU 2014-09 during the first quarter of fiscal 2019. Product Warranty The Company generally provides a one-year warranty for certain products sold in which estimated contractual warranty obligations are recorded as an expense at the time of shipment. The Company’s products are subject to regulatory and quality standards. Future warranty costs are estimated based on historical product performance rates and related costs to repair given products. The accounting estimate related to product warranty expense involves judgment in determining future estimated warranty costs. Should actual performance rates or repair costs differ from estimates, revisions to the estimated warranty liability would be required. Accumulated Other Comprehensive Income (Loss) Comprehensive income (loss) is comprised of net income, plus all changes in equity of a business enterprise during a period from transactions and other events and circumstances from non-owner sources, including any foreign currency translation adjustments. These changes in equity are recorded as adjustments to accumulated other comprehensive income (loss) in the Company’s consolidated balance sheet. The components of accumulated other comprehensive income (loss) consist of foreign currency translation adjustments and changes in unrealized gains (losses) on marketable securities. There were no reclassifications out of accumulated other comprehensive income (loss) during the fiscal years ended March 31, 2018, 2017 and 2016. Translation of Foreign Currencies The functional currency of the Company’s foreign subsidiaries is their local currency. The assets and liabilities of the Company’s foreign subsidiaries are translated into U.S. dollars at exchange rates in effect at the balance sheet date. Income and expense items in the Company’s consolidated statement of operations are translated at the average exchange rates prevailing during the period. The cumulative translation effect for subsidiaries using a functional currency other than the U.S. dollar is included in accumulated other comprehensive income (loss) as a separate component of stockholders’ equity. The Company’s intercompany accounts are denominated in the functional currency of the foreign subsidiary. Gains and losses resulting from the remeasurement of intercompany receivables that the Company considers to be of a long-term investment nature are recorded in accumulated other comprehensive income or loss as a separate component of stockholders’ equity, while gains and losses resulting from the remeasurement of intercompany receivables from those foreign subsidiaries for which the Company anticipates settlement in the foreseeable future are recorded in the consolidated statement of operations. The net foreign currency translation gains and losses recorded in the consolidated statements of operations for the fiscal years ended March 31, 2018, 2017 and 2016 were not significant. Net Income Per Share Basic net income per share is computed by dividing net income by the weighted average number of common shares outstanding during the fiscal year. Diluted net income per share is computed using the treasury stock method by dividing net income by the weighted average number of dilutive common shares outstanding during the fiscal year. Diluted shares outstanding is calculated by adding to the weighted average shares outstanding any potential dilutive securities outstanding for the fiscal year. Potential dilutive securities include stock options, restricted stock units, performance-based restricted stock units and shares to be purchased under the Company’s employee stock purchase plan. In fiscal years when a net loss is reported, all common stock equivalents are excluded from the calculation because they would have an anti-dilutive effect, meaning the loss per share would be reduced. Therefore, in periods when a loss is reported basic and dilutive loss per share are the same. For the fiscal years ended March 31, 2018, 2017 and 2016, the Company’s basic and diluted net income per share were as follows (in thousands, except per share data): Fiscal Years Ended March 31, 2018 2017 2016 Basic Net Income Per Share Net income $ 112,170 $ 52,116 $ 38,147 Weighted average shares used in computing basic net income per share 44,153 43,238 42,204 Net income per share - basic $ 2.54 $ 1.21 $ 0.90 Fiscal Years Ended March 31, 2018 2017 2016 Diluted Net Income Per Share Net income $ 112,170 $ 52,116 $ 38,147 Weighted average shares used in computing basic net income per share 44,153 43,238 42,204 Effect of dilutive securities 1,696 1,420 2,691 Weighted average shares used in computing diluted net income per share 45,849 44,658 44,895 Net income per share - diluted $ 2.45 $ 1.17 $ 0.85 For the fiscal years ended March 31, 2018, 2017 and 2016, approximately 155,000, 24,000 and 62,000 shares of common stock underlying outstanding securities primarily related to out-of-the-money stock options and performance-based awards where milestones were not met were not included in the computation of diluted earnings per share because their inclusion would be anti-dilutive. Stock-Based Compensation The Company’s stock-based compensation cost is measured at the grant date based on the fair value of the award and is recognized as an expense over the requisite service period. The fair value of stock option grants is estimated using the Black-Scholes option pricing model. Use of the valuation model requires management to make certain assumptions with respect to selected model inputs. The risk-free interest rate is based on the U.S. Treasury yield curve in effect at the time of grant for a term consistent with the expected life of the stock options. Volatility assumptions are calculated based on historical volatility of the Company’s stock. The Company estimates the expected term of options based on historical exercise experience and estimates of future exercises of unexercised options. In addition, an expected dividend yield of zero is used in the option valuation model because the Company does not pay cash dividends and does not expect to pay any cash dividends in the foreseeable future. Forfeitures are recorded as they occur instead of estimating forfeitures that are expected to occur. An accounting policy change was made by the Company related to the recording of forfeitures during the quarter ended June 30, 2017 as a result of the adoption of ASU 2016-09, “Compensation – Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting” For awards with service conditions only, the Company recognizes stock-based compensation expense on a straight-line basis over the requisite service period. For awards with service, performance and market-based conditions, the Company recognizes stock-based compensation expense using the graded vesting method over the requisite service period. Estimates of stock-based compensation expense for an award with performance conditions are based on the probable outcome of the performance conditions. The cumulative effect of changes in the probability outcomes are recorded in the period in which the changes occur. For awards with market-based conditions, the Company uses a Monte Carlo simulation model to estimate that the grant-date fair value. The fair value related to market-based awards is recorded as stock-based compensation expense over the vesting period regardless of whether the market condition is achieved or not. Income Taxes The Company’s provision for income taxes is comprised of a current and deferred provision. The current income tax provision is calculated as the estimated taxes payable or refundable on income tax returns for the current fiscal year. The deferred income tax provision is calculated for the estimated future income tax effects attributable to temporary differences and carryforwards using expected tax rates in effect in the years during which the temporary differences are expected to reverse. Deferred income taxes are recognized for the tax consequences in future years as the differences between the tax bases of assets and liabilities and their financial reporting amounts at each fiscal year end based on enacted tax laws and statutory tax rates applicable to the periods in which the differences are expected to impact taxable income. The Company regularly assesses its ability to realize its deferred tax assets. Assessing the realization of deferred tax assets requires significant management judgment. Valuation allowances are established when necessary to reduce net deferred tax assets to the amount that is more likely than not to be realized. The Company recognizes and measures uncertain tax positions using a two-step approach. The first step is to evaluate the tax position for recognition by determining if, based on the technical merits, it is more likely than not that the position will be sustained upon audit, including resolution of related appeals or litigation processes, if any. The second step is to measure the tax benefit at the largest amount that is more likely than not of being realized upon ultimate settlement. The Company reevaluates these uncertain tax positions on an ongoing basis, when applicable. This evaluation is based on factors including, but not limited to, changes in facts or circumstances, new information and technical insights, and changes in tax laws. Any changes in these factors could result in the recognition of a tax benefit or an additional charge to the tax provision. Please refer to “Note 10. Income Taxes” for further information related to the Tax Reform Act (defined below) and its impact on the Company’s financial statements. When applicable, the Company accrues for the effects of uncertain tax positions and the related potential penalties and interest through income tax expense. New Accounting Pronouncements Adopted Effective April 1, 2017, the Company adopted the Financial Accounting Standards Board, FASB, standard update ASU 2016-09, “ Compensation – Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting, The following table summarizes the most significant impacts of ASU 2016-09 for the year ended March 31, 2018: Description of Change: Impact of Change Upon Adoption on April 1, 2017 and for the Year Ended March 31, 2018: Adoption Method: The new standard eliminates the requirement that excess tax benefits be realized through a reduction in income taxes payable before a company can recognize them in the statement of operations. As a result, on April 1, 2017, the Company recorded a cumulative-effect adjustment to increase retained earnings and deferred tax assets by $76.4 million for excess tax benefits not previously recognized. Modified-retrospective (required) Excess tax benefits related to restricted stock unit vestings or stock option exercises are recorded through the statement of operations. The income tax benefit for the year ended March 31, 2018 included excess tax benefits of $31.0 million. These recognized excess tax benefits resulted from restricted stock units that vested or stock options that were exercised during the year ended March 31, 2018. Prospective (required) Excess tax benefits related to restricted stock unit vestings or stock option exercises are classified as operating cash flows instead of financing cash flows. Increase in cash flow from operating activities and decrease in cash flow from financing activities by approximately $31.0 million for the year ended March 31, 2018. The statement of cash flows for the prior period has not been adjusted. Prospective (elected) Calculation of diluted weighted average shares outstanding under the treasury method no longer assume that tax benefits related to stock-based awards are used to repurchase common stock. The Company excluded the related tax benefits when applying the treasury stock method for computing diluted shares outstanding on a prospective basis as required by ASU 2016-09. Prospective (required) An accounting policy election can be made to reduce stock-based compensation expense for forfeitures as they occur instead of estimating forfeitures that are expected to occur. The Company made an accounting policy election to account for forfeitures as they occur with the change applied on a modified retrospective basis with a cumulative effect adjustment on April 1, 2017 to increase additional paid-in capital by $1.8 million, increase deferred tax assets by $0.7 million and decrease retained earnings by $1.1 million. The Company elected to make this accounting policy change to simplify the accounting for stock-based compensation and believes this method provides a more accurate reflection of periodic stock based compensation cost. Prior to the adoption of this accounting standard, the Company estimated at grant the likelihood that the award would ultimately vest, and revised the estimate, if necessary, in future periods if the actual forfeiture rate differed. Modified-retrospective (elected) Cash payments to tax authorities for shares withheld to meet employee tax withholding requirements on restricted stock units are classified as financing cash flow instead of operating cash flow. No change since the Company has historically presented these amounts as a financing activity. Prior to ASU 2016-09, U.S. GAAP has not specified how these types of transactions should be classified in the statement of cash flows. N/A See table below for the changes in beginning stockholders’ equity as a result of this implementation. Common Stock Treasury Stock Number of shares Par value Number of shares Amount Additional Paid in Capital Accumulated Deficit Accumulated Other Comprehensive Income (Loss) Total Stockholders' Equity Balance, March 31, 2017 43,673,286 $ 437 1,575,995 $ (46,763 ) $ 565,962 $ (46,959 ) $ (20,606 ) $ 452,071 Cumulative effect of adoption of new accounting standard 1,835 75,246 77,081 Balance, April 1, 2017 43,673,286 $ 437 1,575,995 $ (46,763 ) $ 567,797 $ 28,287 $ (20,606 ) $ 529,152 Recent Accounting Pronouncements In May 2014, the FASB, issued ASU 2014-09, Revenue from Contracts with Customers The Company established an implementation team to assist with its assessment of the impact of the new revenue guidance on its operations, consolidated financial statements and related disclosures. The Company’s assessment has included performing analysis for each revenue stream identified, assessing the potential differences in recognition and measurement that may result from adopting this standard and assessing whether the Company meets certain practical expedients. Based on the results of the assessment, the adoption of this standard will not have a material impact on the timing or amount of revenue recognized upon adoption and there is no significant cumulative prior period adjustment to be recorded to the opening balance of retained earnings upon adoption. The Company also anticipates changes to its disclosures to comply with the new disclosure requirements. The Company is implementing the necessary changes to its revenue recognition accounting policies and controls to support recognition and disclosure under the new standard. In January 2016, the FASB issued ASU 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities In February 2016, the FASB issued ASU 2016-02, Leases

Cash Equivalents, Marketable Se

Cash Equivalents, Marketable Securities and Fair Value Measurements	12 Months Ended
	Mar. 31, 2018
Fair Value Disclosures [Abstract]
Cash Equivalents Marketable Securities and Fair Value Measurements	Note 3. Cash Equivalents, Marketable Securities and Fair Value Measurements The Company classifies any marketable security with a maturity date of 90 days or less at the time of purchase as a cash equivalent. Cash equivalents are carried on the balance sheet at fair market value. The Company’s marketable securities are classified as available-for-sale securities and, accordingly, are recorded at fair value. The difference between amortized cost and fair value is included in stockholders’ equity. At March 31, 2018 and 2017, the Company’s financial instruments consist primarily of cash and cash equivalents, marketable securities, accounts receivable, accounts payable and contingent consideration. The carrying amounts of accounts receivable and accounts payable are considered reasonable estimates of their fair value, due to the short maturity of these investments. The Company’s cash equivalents and marketable securities at March 31, 2018 and 2017 are classified on the balance sheet as follows: March 31, 2018 March 31, 2017 (in $000's) Cash equivalents (within 90 days at the time of purchase to maturity) $ 22,595 $ 23,975 Short-term marketable securities (within one year to maturity) 319,274 190,908 Long-term marketable securities (one to two years to maturity) 37,502 47,143 $ 379,371 $ 262,026 The Company’s cash equivalents and marketable securities at March 31, 2018 and 2017 are invested in the following: Amortized Gross Unrealized Gross Unrealized Fair Market Cost Gains Losses Value (in $000's) March 31, 2018: Money market funds $ 5,845 $ — $ — $ 5,845 Repurchase agreements 16,750 — — 16,750 Short-term U.S. Treasury mutual fund securities 18,132 — (29 ) 18,103 Short-term government-backed securities 212,255 3 (538 ) 211,720 Short-term corporate debt securities 52,737 — (161 ) 52,576 Short-term commercial paper 36,936 2 (63 ) 36,875 Long-term U.S. Treasury mutual fund securities 10,953 — (16 ) 10,937 Long-term government-backed securities 24,798 1 (12 ) 24,787 Long-term corporate debt securities 1,777 1 — 1,778 $ 380,183 $ 7 $ (819 ) $ 379,371 Amortized Gross Unrealized Gross Unrealized Fair Market Cost Gains Losses Value (in $000's) March 31, 2017: Money market funds $ 11,975 $ — $ — $ 11,975 Repurchase agreements 12,000 — — 12,000 Short-term U.S. Treasury mutual fund securities 45,199 — (13 ) 45,186 Short-term government-backed securities 90,199 1 (87 ) 90,113 Short-term corporate debt securities 13,161 — (6 ) 13,155 Short-term commercial paper 42,304 — (25 ) 42,279 Long-term U.S. Treasury mutual fund securities 1,998 — (3 ) 1,995 Long-term government-backed securities 43,484 5 (18 ) 43,471 Long-term corporate debt securities 1,853 — (1 ) 1,852 $ 262,173 $ 6 $ (153 ) $ 262,026 Fair Value Hierarchy Fair value is defined as the price that would be received upon the sale of an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three categories: Level 1: Quoted market prices in active markets for identical assets or liabilities. Level 2: Observable market based inputs or unobservable inputs that are corroborated by market data. Level 3: Unobservable inputs that are not corroborated by market data. Level 1 primarily consists of financial instruments whose values are based on quoted market prices such as exchange-traded instruments and listed equities. Level 2 includes financial instruments that are valued using models or other valuation methodologies. These models are primarily industry-standard models that consider various assumptions, including time value, yield curve, volatility factors, prepayment speeds, default rates, loss severity, current market and contractual prices for the underlying financial instruments, as well as other relevant economic measures. Substantially all of these assumptions are observable in the marketplace, can be derived from observable data or are supported by observable levels at which transactions are executed in the marketplace. Level 3 is comprised of unobservable inputs that are supported by little or no market activity. Financial assets are considered Level 3 when their fair values are determined using pricing models, discounted cash flows or similar techniques and at least one significant model assumption or input is unobservable. The following table presents the Company’s fair value hierarchy for its financial instruments measured at fair value as of March 31, 2018 and 2017: Level 1 Level 2 Level 3 Total March 31, 2018: (in $000's) Assets Money market funds $ 5,845 $ — $ — $ 5,845 Repurchase agreements — 16,750 — 16,750 Short-term U.S. Treasury mutual fund securities — 18,103 — 18,103 Short-term government-backed securities — 211,720 — 211,720 Short-term corporate debt securities — 52,576 — 52,576 Short-term commercial paper — 36,875 — 36,875 Long-term U.S. Treasury mutual fund securities — 10,937 — 10,937 Long-term government-backed securities — 24,787 — 24,787 Long-term corporate debt securities — 1,778 — 1,778 Liabilities Contingent consideration — — 10,490 10,490 Level 1 Level 2 Level 3 Total March 31, 2017: (in $000's) Assets Money market funds $ 11,975 $ — $ — $ 11,975 Repurchase agreements — 12,000 — 12,000 Short-term U.S. Treasury mutual fund securities — 45,186 — 45,186 Short-term government-backed securities — 90,113 — 90,113 Short-term corporate debt securities — 13,155 — 13,155 Short-term commercial paper — 42,279 — 42,279 Long-term U.S. Treasury mutual fund securities — 1,995 — 1,995 Long-term government-backed securities — 43,471 — 43,471 Long-term corporate debt securities — 1,852 — 1,852 Liabilities Contingent consideration — — 9,153 9,153 The Company has determined that the estimated fair value of its money market funds are reported as Level 1 financial assets as they are valued at quoted market prices in active markets. The Company has determined that the estimated fair value of its U.S. Treasury mutual fund securities, government-backed securities, corporate debt securities, repurchase agreements and commercial paper are reported as Level 2 financial assets as they are not exchange-traded instruments. The Company’s financial liabilities consisted of contingent consideration potentially payable related to the acquisition of ECP Entwicklungsgesellschaft mbH, or ECP and AIS GmbH Aachen Innovative Solutions, or AIS, in July 2014. The Company acquired ECP for $13.0 million in cash, with additional potential payouts totaling $15.0 million based on the achievement of CE Mark approval in the European Union and a revenue-based milestone related to the development of the future Impella ECP TM robabilities were applied to each potential scenario and the resulting values were discounted using a rate that considers weighted average cost of capital as well as a specific risk premium associated with the riskiness of the earn out itself, the related projections, and the overall business. The r This liability is reported as Level 3 as the estimated fair value of the contingent consideration related to the acquisition of ECP requires significant management judgment or estimation and is calculated using the following valuation methods: Fair Value at March 31, 2018 (in $000's) Valuation Methodology Significant Unobservable Input Weighted Average (range, if applicable) Clinical and regulatory milestone $ 5,631 Probability weighted income approach Projected fiscal year of milestone payments 2019 to 2022 Discount rate 3.2% to 3.8% Probability of occurrence Probability adjusted level of 40% for the base case scenario and 12% to 30% for various upside and downside scenarios Revenue-based milestone 4,859 Monte Carlo simulation model Projected fiscal year of milestone payments 2023 to 2035 Discount rate 18% Expected volatility for forecasted revenues 50% Probability of payment (risk-neutral) 78.5% $ 10,490 The following table summarizes the change in fair value, as determined by Level 3 inputs, of the contingent consideration for the fiscal years ended March 31, 2018, 2017 and 2016: Fiscal Years Ended March 31, 2018 2017 2016 (in $000's) Level 3 liabilities, beginning balance $ 9,153 $ 7,563 $ 6,510 Additions — — — Payments — — — Change in fair value 1,337 1,590 1,053 Level 3 liabilities, ending balance $ 10,490 $ 9,153 $ 7,563 The change in fair value of the contingent consideration was primarily due to the passage of time on the fair value measurement of milestones related to the ECP acquisition. Adjustments associated with the change in fair value of contingent consideration are included in research and development expenses in the Company’s consolidated statements of operations. Significant increases or decreases in any of the probabilities of success or changes in expected timelines for achievement of any of these milestones could result in a significantly higher or lower fair value of the liability. The fair value of the contingent consideration at each reporting date is updated by reflecting the changes in fair value reflected in the Company’s consolidated statement of operations. There is no assurance that any of the conditions for the milestone payments will be met. Other Investments The Company periodically makes investments in private medical device companies that focus on heart failure, heart pump and other medical device technologies. The aggregate carrying amount of the Company’s portfolio of other investments was $12.6 million and $7.2 million at March 31, 2018 and 2017, respectively, and is classified within other assets in the consolidated balance sheets. During the years ended March 31, 2018 and 2017, respectively, the Company made investments of $6.4 million and $2.9 million in private medical device companies. The Company determined that it is not practicable to estimate the fair value of these investments. As such, these investments are accounted for using the cost method and are evaluated for impairment and measured at fair value only if there are identified events or changes in circumstances that may have a significant adverse effect on the fair value of these investments.

Accounts Receivable

Accounts Receivable	12 Months Ended
	Mar. 31, 2018
Receivables [Abstract]
Accounts Receivable	Note 4. Accounts Receivable The components of accounts receivable are as follows: March 31, 2018 March 31, 2017 (in $000's) Trade receivables $ 70,330 $ 54,337 Allowance for doubtful accounts (320 ) (282 ) $ 70,010 $ 54,055 The following table summarizes activity in the Company's allowance for doubtful accounts: Fiscal Years Ended March 31, 2018 2017 2016 (in $000's) Balance at beginning of year $ 282 $ 124 $ 177 Additions 38 159 42 Write-offs — (1 ) (95 ) Balance at end of year $ 320 $ 282 $ 124

Inventories

Inventories	12 Months Ended
	Mar. 31, 2018
Inventory Disclosure [Abstract]
Inventories	Note 5. Inventories The components of inventories are as follows: March 31, 2018 March 31, 2017 (in $000's) Raw materials and supplies $ 16,481 $ 9,784 Work-in-progress 23,179 16,504 Finished goods 10,544 8,643 $ 50,204 $ 34,931 The Company’s inventories relate to its Impella® product platform. Finished goods and work-in-process inventories consist of direct material, labor and overhead.

Property and Equipment

Property and Equipment	12 Months Ended
	Mar. 31, 2018
Property Plant And Equipment [Abstract]
Property and Equipment	Note 6. Property and Equipment The components of property and equipment are as follows: March 31, 2018 March 31, 2017 (in $000's) Land $ 7,680 $ 4,046 Building and building improvements 63,700 10,900 Capital lease asset — 16,784 Leasehold improvements 2,905 34,854 Machinery and equipment 42,787 27,989 Furniture and fixtures 8,104 3,899 Construction in progress 19,850 9,257 Total cost 145,026 107,729 Less accumulated depreciation (27,859 ) (19,952 ) $ 117,167 $ 87,777 In October 2017, the Company acquired its corporate headquarters that it had been leasing in Danvers, Massachusetts. The total acquisition cost for the land and building was approximately $16.5 million, with $3.0 million being recorded to land and $13.0 million being recorded to building and building improvements. In addition, the Company reclassified $32.6 million in leasehold improvements to building and building improvements due to the termination of the lease agreement upon the property acquisition. In February 2017, the Company acquired its existing European headquarters in Aachen, Germany, consisting of 33,000 square feet of space. The acquisition cost for the land and building was approximately $12.6 million, with $4.0 million being recorded to land and $8.6 million being recorded to the building and building improvements. Depreciation expense related to property and equipment was $11.0 million, $6.2 million, and $3.3 million for the fiscal years ending March 31, 2018, 2017 and 2016, respectively.

Goodwill and In-Process Researc

Goodwill and In-Process Research and Development	12 Months Ended
	Mar. 31, 2018
Goodwill And Intangible Assets Disclosure [Abstract]
Goodwill and In-Process Research and Development	Note 7. Goodwill and In-Process Research and Development The carrying amount of goodwill at March 31, 2018 and 2017 was $35.8 million and $31.0 million, respectively, and has been recorded in connection with the Company’s acquisition of Impella Cardiosystems AG, or Impella, in May 2005 and ECP and AIS in July 2014. The goodwill activity is as follows: (in $000's) Balance at March 31, 2016 $ 33,003 Foreign currency translation impact (1,958 ) Balance at March 31, 2017 $ 31,045 Foreign currency translation impact 4,763 Balance at March 31, 2018 $ 35,808 The Company has no accumulated impairment losses on goodwill. The Company performed a qualitative assessment during the annual impairment review for fiscal 2018 as of October 31, 2017 and concluded that it is not more likely than not that the fair value of the Company’s single reporting unit is less than its carrying amount. Therefore, the two-step goodwill impairment test for the reporting unit was not necessary in fiscal 2018. In July 2014, the Company acquired ECP and AIS and recorded $18.5 million of IPR&D assets. The estimated fair value of the IPR&D assets was determined using a probability-weighted income approach, which discounts expected future cash flows to present value. The projected cash flows for the future Impella ECP TM The carrying value of the Company’s IPR&D assets and the change in the balance for the fiscal years ended March 31, 2018 and 2017 is as follows: (in $000's) Balance at March 31, 2016 $ 15,396 Foreign currency translation impact (914 ) Balance at March 31, 2017 $ 14,482 Foreign currency translation impact 2,223 Balance at March 31, 2018 $ 16,705 The Company tests IPR&D assets for impairment at least annually, or more frequently if impairment indicators exist, by first assessing qualitative factors to determine whether it is more likely than not that the fair value of the IPR&D assets is less than its carrying amount. The Company performed its annual impairment review for fiscal 2018 as of October 31, 2017 and concluded that it is not more likely than not that the fair value of the IPR&D assets is less than its carrying amount.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Mar. 31, 2018
Equity [Abstract]
Stockholders' Equity	Note 8. Stockholders’ Equity Class B Preferred Stock The Company has authorized 1,000,000 shares of Class B Preferred Stock, $.01 par value, of which the Board of Directors can set the designation, rights and privileges. No shares of Class B Preferred Stock have been issued or are outstanding.

Stock Award Plans and Stock-Bas

Stock Award Plans and Stock-Based Compensation	12 Months Ended
	Mar. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock Award Plans and Stock-Based Compensation	Note 9. Stock Award Plans and Stock-Based Compensation Stock Award Plans The Company grants stock options and restricted stock awards to employees and others. All outstanding stock options of the Company as of March 31, 2018 were granted with an exercise price equal to the fair market value on the date of grant. Outstanding stock options, if not exercised, expire 10 years from the date of grant. 2015 Stock Incentive Plan The Company’s 2015 Stock Incentive Plan (the “2015 Plan”) authorizes the grant of a variety of equity awards to the Company’s officers, directors, employees, consultants and advisers, including awards of unrestricted and restricted stock, restricted stock units, incentive and nonqualified stock options to purchase shares of common stock, performance share awards and stock appreciation rights. The 2015 Plan provides that options may only be granted at the current market value on the date of grant. Each share of stock issued pursuant to a stock option or stock appreciation right counts as one share against the maximum number of shares issuable under the 2015 Plan, while each share of stock issued pursuant to any other type of award counts as 1.8 shares against the maximum number of shares issuable under the 2015 Plan. The Company’s policy for issuing shares upon exercise of stock options or the vesting of its restricted stock awards and restricted stock units is to issue shares of common stock at the time of exercise or conversion. At March 31, 2018, a total of approximately 2,542,000 shares were available for future issuance under the 2015 Plan. 2008 Stock Incentive Plan The Company’s 2008 Stock Incentive Plan (the “2008 Plan”) authorizes the grant of a variety of equity awards to the Company’s officers, directors, employees, consultants and advisers, including awards of unrestricted and restricted stock, restricted stock units, incentive and nonqualified stock options to purchase shares of common stock, performance share awards and stock appreciation rights. The 2008 Plan provides that options may only be granted at the current market value on the date of grant. Each share of stock issued pursuant to a stock option or stock appreciation right counts as one share against the maximum number of shares issuable under the 2008 Plan, while each share of stock currently issued pursuant to any other type of award counts as 1.58 shares against the maximum number of shares issuable under the 2008 Plan. The Company’s policy for issuing shares upon exercise of stock options or the vesting of its restricted stock awards and restricted stock units is to issue shares of common stock at the time of exercise or conversion. At March 31, 2018, a total of approximately 270,000 shares were available for future issuance under the 2008 Plan. Stock-Based Compensation The following table summarizes stock-based compensation expense by financial statement line item in the Company’s consolidated statements of operations for the fiscal years ended March 31, 2018, 2017 and 2016: Fiscal Years Ended March 31, 2018 2017 2016 (in $000's) Cost of revenue $ 1,721 $ 1,061 $ 895 Research and development 5,895 6,050 3,950 Selling, general and administrative 32,737 25,755 24,208 $ 40,353 $ 32,866 $ 29,053 The components of stock-based compensation for the fiscal years ended March 31, 2018, 2017 and 2016 were as follows: Fiscal Years Ended March 31, 2018 2017 2016 (in $000's) Restricted stock units $ 34,559 $ 26,570 $ 23,708 Stock options 5,202 5,829 4,866 Employee stock purchase plan 592 467 479 $ 40,353 $ 32,866 $ 29,053 Stock Options The following table summarized stock option activity for the fiscal year ended March 31, 2018: Weighted Weighted Average Aggregate Average Remaining Intrinsic Options Exercise Contractual Value (in thousands) Price Term (years) (in thousands) Outstanding at beginning of period 1,646 $ 32.09 5.46 Granted 155 143.52 Exercised (460 ) 20.23 Cancelled and expired (59 ) 98.21 Outstanding at end of period 1,282 $ 46.81 5.31 $ 313,158 Exercisable at end of period 965 $ 24.88 4.29 $ 256,891 Options vested and expected to vest at end of period 1,259 $ 46.18 5.27 $ 308,252 Stock options generally vest and become exercisable annually over three years. The remaining unrecognized stock-based compensation expense for unvested stock option awards at March 31, 2018 was approximately $9.5 million and the weighted-average period over which this cost will be recognized is 2.2 years. The aggregate intrinsic value of options exercised for fiscal years 2018, 2017 and 2016 was $66.4 million, $74.8 million and $58.6 million, respectively. The total cash received as a result of employee stock option exercises during the fiscal years ended March 31, 2018, 2017 and 2016 was approximately $9.3 million, $10.7 million and $9.8 million, respectively. The Company estimates the fair value of each stock option granted at the grant date using the Black-Scholes option valuation model. The weighted average grant-date fair values and weighted average assumptions used in the calculation of fair value of options granted during the fiscal years ended March 31, 2018, 2017 and 2016 was as follows: Fiscal Years Ended March 31, 2018 2017 2016 Valuation assumptions: Weighted average grant-date fair value $ 52.34 $ 42.40 $ 29.57 Risk-free interest rate 1.87 % 1.41 % 1.55 % Expected option life (years) 4.07 4.14 4.15 Expected volatility 43.5 % 48.9 % 49.7 % The risk-free interest rate is based on the U.S. Treasury yield curve in effect at the time of grant for a term consistent with the expected life of the stock options. Volatility assumptions are calculated based on the historical volatility of the Company’s stock. The Company estimates the expected term of options based on historical exercise experience and estimates of future exercises of unexercised options. An expected dividend yield of zero is used in the option valuation model because the Company does not pay cash dividends and does not expect to pay any cash dividends in the foreseeable future. Forfeitures are recorded as they occur instead of estimating forfeitures that are expected to occur. An accounting policy change was made related to the recording of forfeitures during the quarter ended June 30, 2017 as a result of the adoption of ASU 2016-09, “Compensation – Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting” Restricted Stock Units The following table summarizes restricted stock unit activity for the fiscal year ended March 31, 2018: Number of Shares Weighted Average Grant Date Fair Value (in thousands) (per share) Restricted stock units at beginning of period 1,056 $ 80.50 Granted 296 $ 137.40 Vested (372 ) $ 53.40 Forfeited (100 ) $ 98.47 Restricted stock units at end of period 880 $ 109.01 Restricted stock units generally vest annually over three years. The remaining unrecognized compensation expense for outstanding restricted stock units, including performance-based awards, as of March 31, 2018 was $32.2 million and the weighted-average period over which this cost will be recognized is 1.8 years. The weighted average grant-date fair value for restricted stock units granted during the fiscal years ended March 31, 2018, 2017 and 2016 was $137.40, $97.43 and $87.45 per share, respectively. The total fair value of restricted stock units vested in fiscal years 2018, 2017 and 2016 was $51.0 million, $51.3 million and $39.6 million, respectively. Performance and Market-Based Awards Restricted stock units include certain awards that vest subject to certain performance and market-based criteria. The remaining unrecognized compensation expense for outstanding performance and market-based restricted stock units as of March 31, 2018 was $14.5 million and the weighted-average period over which this cost will be recognized is 1.8 years. Performance-Based Awards In May 2017, performance-based awards of restricted stock units for the potential issuance of 159,000 shares of common stock were issued to certain executive officers and employees, which vest upon achievement of prescribed service milestones by the award recipients and performance milestones by the Company. The Company met the prescribed performance milestones in fiscal 2018 such that the remaining outstanding 152,000 shares of common stock as of March 31, 2018 will vest subject to service requirements for vesting for these employees and stock-based compensation expense is being recognized accordingly over the employee’s service term. In May 2016, performance-based awards of restricted stock units for the potential issuance of 190,890 shares of common stock were issued to certain executive officers and employees, which vest upon achievement of prescribed service milestones by the award recipients and performance milestones by the Company. The Company met a portion of the prescribed performance milestones in fiscal 2017 such that the remaining outstanding 82,000 shares of common stock as of March 31, 2018 will vest subject to service requirements for vesting for these employees and stock-based compensation expense is being recognized accordingly over the employee’s service term. In May 2015, performance-based awards of restricted stock units for the potential issuance of 183,940 shares of common stock were issued to certain executive officers and employees, which vest upon achievement of prescribed service milestones by the award recipients and performance milestones by the Company. The Company met the prescribed performance milestones in fiscal 2016 such that the remaining outstanding 55,000 shares of common stock as of March 31, 2018 will vest subject to service requirements for vesting for these employees and stock-based compensation expense is being recognized accordingly over the employee’s service term. Market-Based Awards In June 2015, the Company awarded certain executive officers a total of up to 322,980 market-based restricted share units, of which 281,530 units remain outstanding. These restricted stock units will vest and result in the issuance of common stock based on continuing employment and the relative ranking of the total shareholder return, or TSR of the Company’s common stock in relation to the TSR of the component companies in the S&P Health Care Equipment Select Industry Index over a three-year performance period based on a comparison of average closing stock prices between June 2015 and June 2018. The actual number of market-based restricted stock units that may be earned can range from 0% to 300% of the target number of shares. One-half of the market-based restricted stock units earned will vest in June 2018 and the remaining restricted stock units will vest one year thereafter provided the executive officers are still employed with the Company. In November 2016, the Company awarded an executive officer a total of up to 41,526 restricted stock units. The restricted stock units are subject to both performance-and time-based vesting. These restricted stock units will vest and result in the issuance of common stock based on continuing employment, the Company achieving positive net profits measured in the aggregate over the first four full fiscal quarters following the grant date and the relative ranking of the TSR of the Company’s common stock in relation to the TSR of the component companies in the S&P Health Care Equipment Select Industry Index over a three-year performance period based on a comparison of average closing stock prices in June 2015 and June 2018. The actual number of restricted stock units that may be earned ranges from 0% to 100% of the target number of shares. One-half of the restricted stock units will potentially vest in June 2018 based on performance criteria described above and the remaining half of the restricted stock units will vest one year thereafter. The Company used a Monte Carlo simulation model to estimate the grant-date fair value of the restricted stock units granted in June 2015 and November 2016. The fair value related to the restricted stock units is being recorded as stock compensation expense over the period from date of grant to June 2019 regardless of the actual TSR outcome achieved. The table below sets forth the assumptions used to value the market-based awards and the estimated grant-date fair value: June 2015 Awards November 2016 Awards Risk-free interest rate 1.10 % 0.90 % Dividend yield 0 % 0 % Remaining performance period (years) 0.21 0.21 Expected volatility 47.2 % 50.6 % Estimated grant date fair value (per share) $ 93.49 - 107.10 $ 62.55 Target performance (number of shares) 107,660 41,526 Employee Stock Purchase Plan The Company has an employee stock purchase plan, or ESPP. Under the ESPP, eligible employees, including officers and directors, who have completed at least three months of employment with the Company or its subsidiaries who elect to participate in the purchase plan instruct the Company to withhold a specified amount of the employee’s income each payroll period during a six-month payment period (the periods April 1—September 30 and October 1—March 31). On the last business day of each six-month payment period, the amount withheld is used to purchase shares of the Company’s common stock at an exercise price equal to 85% of the lower of its market price on the first business day or the last business day of the payment period.

Income Taxes

Income Taxes	12 Months Ended
	Mar. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	Note 10. Income Taxes On December 22, 2017, the Tax Cuts and Jobs Act, or the Tax Reform Act, was signed into law. The Tax Reform Act included significant changes to existing law, including among other items, a reduction to the U.S. federal statutory corporate tax rate from 35% to 21% effective January 1, 2018. ASC 740, Income Taxes (Topic 740) T the income tax provision for the year ended March 31, 2018 The blended U.S. federal statutory corporate tax rate of 31.5% represents the average rate between the pre-enactment U.S. federal statutory corporate tax rate of 35% prior to the January 1, 2018 effective date and the post-enactment U.S. federal statutory corporate tax rate of 21% thereafter. The Company’s income tax provision was $48.3 million, $39.2 million and $27.7 million for the fiscal years ended March 31, 2018, 2017 and 2016, respectively. The Company’s effective tax rate was 30.1%, 43.0% and 42.1% for the fiscal years ended March 31, 2018, 2017 and 2016. Consistent with guidance issued by the U.S. Securities and Exchange Commission, or SEC, which provides for a measurement period of one year from the enactment date to finalize the accounting for effects of the Tax Reform Act, the Company provisionally recorded an income tax expense adjustment of $21.4 As The components of the Company’s income tax provision for the fiscal years ended March 31, 2018, 2017 and 2016 are as follows: 2018 2017 2016 (in $000's) Income before provision for income taxes: United States $ 134,006 $ 78,172 $ 54,406 Foreign 26,431 13,170 11,432 Income before income taxes $ 160,437 $ 91,342 $ 65,838 Current tax expense: Federal $ 752 $ 7,313 $ 1,690 State 1,491 5,045 2,113 Foreign 3,400 1,066 1,592 5,643 13,424 5,395 Deferred tax expense (benefit): Federal 38,848 23,008 18,769 State (1,014 ) (349 ) 1,284 Foreign 4,790 3,144 2,243 42,624 25,803 22,296 Total income tax provision $ 48,267 $ 39,227 $ 27,691 The components of the Company’s net deferred taxes were as follows: March 31, 2018 2017 (in $000's) Deferred tax assets Non-operating loss and tax credit carryforwards $ 48,724 $ 8,814 Stock-based compensation 13,271 16,560 Nondeductible reserves and accruals 8,290 10,303 Foreign non-operating loss carryforwards 9,598 13,634 Deferred revenue 3,770 4,308 Depreciation and amortization 826 2,135 Other, net 822 1,308 85,301 57,062 Deferred tax liabilities Goodwill (6,787 ) (9,444 ) In-process research and development (5,045 ) (4,374 ) Depreciation (1,011 ) — Domestic deferred tax liability on foreign non-operating loss carryforwards (963 ) (6,836 ) (13,806 ) (20,654 ) Net deferred tax assets 71,495 36,408 Valuation allowance (1,652 ) (2,468 ) Net deferred tax assets $ 69,843 $ 33,940 Reported as: Long-term deferred tax assets, net $ 70,746 $ 34,723 Long-term deferred tax liabilities (903 ) (783 ) Net deferred tax assets $ 69,843 $ 33,940 A reconciliation of the federal statutory income tax rate to the Company’s effective income tax rate is as follows for the fiscal years ended March 31, 2018, 2017, and 2016: 2018 2017 2016 Statutory income tax rate 31.5 % 35.0 % 35.0 % (Decrease) increase resulting from: Change in valuation allowance 0.5 0.2 0.7 Credits (4.9 ) (3.3 ) (4.1 ) Foreign taxes 2.2 2.0 2.5 State taxes, net 2.0 3.8 3.7 Permanent differences 2.4 3.3 3.0 Stock-based compensation (17.2 ) 0.2 0.3 Rate differential on foreign operations — 0.1 — Effect of the Tax Reform Act on net deferred tax assets 13.0 — — Other 0.6 1.7 1.0 Effective tax rate 30.1 % 43.0 % 42.1 % The Company regularly assesses its ability to realize its deferred tax assets. Assessing the realization of deferred tax assets requires significant management judgment. In determining whether its deferred tax assets are more likely than not realizable, the Company evaluates all available positive and negative evidence, and weights the evidence based on its objectivity. As of March 31, 2018 and 2017, respectively, the Company maintained a valuation allowance of $1.7 million and $2.5 million for deferred tax assets primarily related to non-operating loss, or NOL, carryforwards in certain foreign jurisdictions in which the Company has had limited or no history of profitability. Based on the review of all available evidence, the Company recorded a valuation allowance to reduce these deferred tax assets to the amount that is more likely than not to be realizable as of March 31, 2018 and 2017. Changes in the valuation allowance for deferred tax assets during the fiscal years ended March 31, 2018, 2017 and 2016 were as follows: 2018 2017 2016 (in $000's) Balance at beginning of year $ 2,468 $ 2,418 $ 2,912 Increases 325 50 677 Decreases (1,141 ) — (1,171 ) Balance at end of year $ 1,652 $ 2,468 $ 2,418 At March 31, 2018, the Company had NOLs, of approximately $72.2 million which expire in varying years from fiscal 2019 through fiscal 2035. At March 31, 2018, the Company had foreign NOLs of approximately $3.9 million, primarily in Germany and France, which do not expire. In addition, at March 31, 2018, the Company had federal and state research and development credit carryforwards of approximately $16.6 million and $9.0 million, respectively, which expire in varying years from fiscal 2019 through fiscal 2038. As of March 31, 2018 and 2017, the Company has no material uncertain tax positions and no interest and penalties were recognized during the years ended March 31, 2018, 2017 and 2016, respectively. The Company and its subsidiaries are subject to U.S. federal income tax, as well as income tax of multiple state and foreign jurisdictions. Fiscal years 2012 through 2017 remain open to examination in Germany and Abiomed Europe GmbH, the Company’s main operating subsidiary in Germany, is currently being audited for fiscal years 2012 through 2015. In July 2017, the Company was notified by the Internal Revenue Service, or IRS, that it has selected the Company’s federal tax return for fiscal 2016 for examination. In September 2017, the Company was notified by German tax authorities that our ECP subsidiary in Germany will be audited for the year ended December 31, 2014 and the three months ended March 31, 2015. The ECP audit was completed in fiscal 2018 and no adjustments were made as a result of the audit. All tax years remain subject to examination by the IRS and state tax authorities, because the Company has net operating loss and tax credit carryforwards which may be utilized in future years to offset taxable income, those years may also be subject to review by relevant taxing authorities if the carryforwards are utilized.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Mar. 31, 2018
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	Note 11. Commitments and Contingencies Commitments Leases The Company’s corporate headquarters is located in Danvers, Massachusetts. This facility encompasses most of the Company’s U.S. operations, including research and development, manufacturing, sales and marketing and general and administrative departments. In October 2017, the acquired its corporate headquarters for approximately $16.5 million and terminated its existing lease arrangement (See Note 6). Future minimum lease payments under non-cancelable leases as of March 31, 2018 are approximately as follows: Fiscal Years Ending March 31, Operating Leases (in $000s) 2019 $ 2,078 2020 1,888 2021 1,901 2022 1,408 2023 891 Thereafter 1,923 Total minimum lease payments $ 10,089 In February 2017, the Company entered into a lease agreement for an additional 21,603 square feet of office space in Danvers, Massachusetts which expires on July 31, 2022. In December 2017, the Company entered into an amendment to this lease to extend the term through August 31, 2025 and to add an additional 6,607 square feet of space in which rent would begin around June 1, 2018. The amendment also allows the Company a right of first offer to purchase the property from January 1, 2018 through August 31, 2035, if the lessor decides to sell the building or receives an offer to purchase the building from a third-party buyer. In March 2018, the Company entered into an amendment to the lease to add an additional 11,269 square feet of space for which rent will begin on or around June 1, 2018 through August 31, 2025. The annual rent expense for this lease agreement is estimated to be $0.4 million. In September 2016, the Company entered into a lease agreement in Berlin, Germany which commenced in May 2017 and expires in May 2024. The annual rent expense for the lease is estimated to be $0.3 million. In October 2016, the Company entered into a lease agreement for an office in Tokyo, Japan and expires in September 2021. The office houses administrative, regulatory, and training personnel in connection with the Company’s commercial launch in Japan. The annual rent expense for the lease is estimated to be $0.9 million. License Agreements In April 2014, the Company entered into an exclusive license agreement for the rights to certain optical sensor technologies in the field of cardio-circulatory assist devices. Pursuant to the terms of the license agreement, the Company agreed to make potential payments of $6.0 million. Through March 31, 2018, the Company has made $3.5 million in milestones payments which included a $1.5 million upfront payment upon the execution of the agreement. Any potential future milestone payment amounts have not been included in the contractual obligations table above due to the uncertainty related to the successful achievement of these milestones. Contingencies From time to time, the Company is involved in legal and administrative proceedings and claims of various types. In some actions, the claimants seek damages, as well as other relief, which, if granted, would require significant expenditures. The Company records a liability in its consolidated financial statements for these matters when a loss is known or considered probable and the amount can be reasonably estimated. The Company reviews these estimates each accounting period as additional information is known and adjusts the loss provision when appropriate. If a matter is both probable to result in liability and the amount of loss can be reasonably estimated, the Company estimates and discloses the possible loss or range of loss. If the loss is not probable or cannot be reasonably estimated, a liability is not recorded in its consolidated financial statements. Settlement Agreement On April 25, 2014, the Company received an administrative subpoena from the Boston regional office of the United States Department of Health and Human Services Office of Inspector General, or HHS-OIG, requesting materials relating to the Company’s reimbursement of employee expenses and remuneration to healthcare providers from July 2012 through December 2012, in connection with a civil investigation under the False Claims Act. Subsequently, the Company received Civil Investigative Demands from the U.S. Attorney’s Office for the District of Massachusetts, or the DOJ, that collectively sought additional information relating to this matter for the time period of January 1, 2011 through September 14, 2016. DOJ’s investigation derived from a civil qui tam action, United States ex rel. Max Bennett v. Abiomed, 13-cv-12277, filed on behalf of the United States and certain individual states in the District of Massachusetts by a former employee. The complaint alleged violations of the Federal False Claims Act and analogous state false claims acts, as well as claims that the Company retaliated against Bennett in violation of federal and state law. On March 6, 2018, the Company entered a Settlement Agreement (the “Settlement Agreement”) with the DOJ, on behalf of HHS-OIG, and Bennett to resolve the claims relating to the Company’s reimbursement of employee expenses for meals with healthcare providers. Under the terms of the Settlement Agreement, the Company agreed to pay $3.1 million, plus approximately $30,000 of accrued interest, to the U.S. government. The Company also agreed to pay $150,000 to the former Company employee in settlement of his claims for reasonable expenses, costs and attorneys’ fees. The Settlement Agreement contained no admission of liability on the part of the Company and did not require the Company to enter into a corporate integrity agreement. Pursuant to the Settlement Agreement, the U.S. government and the former Company employee agreed to release the Company from civil monetary liability arising from allegations that it caused third parties to submit false claims for payment to Medicare. In connection with the resolution, the various state claims were dismissed without prejudice. The Settlement Agreement did not resolve the former Company employee’s individual claims of employment retaliation, against which the Company intends to defend vigorously. The Company is not able to predict whether or how the former Company employee’s remaining claims might be resolved, or their potential impact on the Company’s financial position. Thoratec Matters Thoratec Corporation, or Thoratec, a subsidiary of Abbott Laboratories, has challenged a number of Company owned patents in Europe in connection with the launch of their HeartMate PHP medical device, or PHP, in Europe. These actions relate to Thoratec’s ability to manufacture and sell their PHP product in Europe. These actions do not relate to the Company’s ability to manufacture or sell its Impella line of devices. In December 2014, Thoratec filed a nullity suit in the German Federal Patent Court against a German “pigtail” patent owned by the Company with a flexible extension feature, and auxiliary pigtail, basket and funnel features. The validity hearing was held in November 2016 and the Federal Patent Court found the patent invalid. The Company is appealing this decision. In August 2015, Thoratec filed a nullity action in the German Federal Patent Court against two Company owned patents covering a “magnetic clutch” feature. These magnetic clutch patents were acquired by the Company in July 2014, in connection with its acquisition of ECP and AIS. The validity hearing for the magnetic clutch patents was held in June 2017. The Company’s patents were upheld in an amended form to focus on the structure and interaction of the magnets in the clutch. The Federal Patent Court found certain unamended claims to be invalid. The Company is appealing the decision with respect to the unamended claims. In September 2015, the Company filed counterclaims in the magnetic clutch action in Germany asserting that the PHP product infringes the two magnetic clutch patents, a European pigtail patent, and the German pigtail patent. The infringement trial has been stayed, pending resolution of the German nullity actions. In February 2017, Thoratec filed an opposition in the European Patent Office against a Company owned patent acquired in connection with the acquisition of ECP and AIS relating to a housing structure for an expandable pump. The Company filed an initial response to the opposition in July 2017. Oral proceedings are scheduled for October 26, 2018. In December 2017, Thoratec filed an opposition in the European Patent Office against a Company owned patent acquired in connection with the acquisition of ECP and AIS relating to a pump having a shaft cap with an atraumatic ball. The Company’s due date for responding to the opposition is May 27, 2018. Maquet Matters In December 2015, the Company received a letter from Maquet Cardiovascular LLC, or Maquet, a subsidiary of the Getinge Group, asserting that the Company’s Impella devices infringe certain claims having guidewire, lumen and sensor features, which were in two Maquet patents and one pending patent application in the U.S. and elsewhere, and attached a draft litigation complaint and encouraged the Company to take a license from Maquet. In January 2016, the Company responded to Maquet stating that it believed that the cited claims were invalid and that its Impella devices did not infringe the cited patents. In May 2016, Maquet notified the Company that its pending U.S. patent application had been issued as a U.S. patent, repeated their earlier assertion and encouraged the Company to discuss taking a license from Maquet. The three patents expire September 2020, December 2020 and October 2021. In May 2016, the Company filed suit in U.S. District Court for the District of Massachusetts, or D. Mass., against Maquet seeking a declaratory judgment that the Company’s Impella devices do not infringe Maquet’s cited patent rights. In August 2016, Maquet sent a letter to the Company identifying four new U.S. continuation patent filings with claims that Maquet alleges are infringed by the Company’s Impella devices. Of the four U.S. continuation applications, one issued as a patent on January 17, 2017, one issued as a patent on February 7, 2017, one issued as a patent on March 21, 2017, and one issued as a patent on October 17, 2017. These four issued patents will expire in September 2020. In September 2016, Maquet filed a response to the Company’s suit in D. Mass., including various counterclaims alleging that the Company’s Impella 2.5, Impella CP, Impella 5.0, and Impella RP heart pumps infringe certain claims of the three original issued U.S. patents (“2016 action”). On June 15, 2017, Maquet filed a motion for leave to amend its infringement counterclaims to add the first three additional U.S. continuation patents mentioned above and to file various false advertising, unfair competition claims under state law and under the Lanham Act, and a trademark cancellation in the pending case. Maquet’s amended complaint and counterclaim, like those it originally filed, seek injunctive relief and monetary damages in the form of a reasonable royalty, with three times the amount for alleged willful infringement. The amended complaint admits that Maquet’s currently commercially available products do not embody the claims of the asserted patents. On July 21, 2017, the Court granted the motion in part, allowing the three additional continuation patents to be added to the case, but denying addition of the false advertising claims, Lanham Act claims, and the trademark cancellation claims. On October 26, 2017, Maquet filed an amended answer, adding a new counterclaim alleging infringement of an additional seventh patent. Maquet did not seek leave to amend the pleadings and did not first consult with the Company concerning this addition. On November 11, 2017, after Maquet refused to withdraw the patent, the Company filed a motion to strike Maquet’s counterclaims regarding the seventh patent on the grounds that Maquet did not seek leave to add the patent and had amended its pleadings after the deadline set by the Court. On November 15, 2017, Maquet informed the Court that it would agree to voluntarily withdraw the seventh patent. On November 22, 2017, Maquet filed a second lawsuit in D. Mass alleging that the Company’s Impella 2.5, Impella CP, and Impella 5.0 heart pumps infringe certain claims of the seventh patent (“2017 action”). In the complaint, Maquet seeks injunctive relief and monetary damages in the form of a reasonable royalty, with three times the amount for alleged willful infringement. With regard to the first six Maquet patents mentioned above, in March and April 2017, the Company filed requests for inter partes review, or IPR, at the U.S. Patent & Trademark Office’s Patent Trial and Appeals Board, or PTAB, asserting that the claims are invalid in view of prior art blood pump technology. In September and October 2017, the PTAB denied institution on these IPR requests filed by the Company. In September 2017, the Company filed additional IPRs and in March and April 2018, the PTAB denied institution of these IPR petitions. The Company cannot estimate what the potential outcome of these claims will be at this time. In the 2016 action, discovery is ongoing and, after the Court conducted a Markman hearing on claim interpretation in April 2018, the decision on claim interpretation is still pending. No schedule has been set in the 2017 action. The Company is unable to estimate the potential liability with respect to the legal matters noted above. There are numerous factors that make it difficult to meaningfully estimate possible loss or range of loss at this stage of the legal proceedings, including that patent disputes with Thoratec and Maquet remain either in relatively early stages, or there are significant factual and legal issues to be resolved and information obtained or rulings made during any lawsuits or investigations that could affect the methodology for calculation.

Accrued Expenses

Accrued Expenses	12 Months Ended
	Mar. 31, 2018
Payables And Accruals [Abstract]
Accrued Expenses	Note 12. Accrued Expenses Accrued expenses consisted of the following: March 31, 2018 March 31, 2017 (in $000's) Employee compensation $ 30,330 $ 23,290 Sales and income taxes 4,562 3,180 Research and development 3,162 2,349 Marketing 2,305 1,827 Professional, legal and accounting fees 1,870 2,019 Warranty 1,081 717 Accrued capital expenditures 250 2,300 Other 2,587 2,021 $ 46,147 $ 37,703 Employee compensation consists primarily of accrued bonuses, accrued commissions and accrued employee benefits at March 31, 2018 and 2017.

Segment and Enterprise Wide Dis

Segment and Enterprise Wide Disclosures	12 Months Ended
	Mar. 31, 2018
Segment Reporting [Abstract]
Segment and Enterprise Wide Disclosures	Note 13. Segment and Enterprise Wide Disclosures The Company operates in one business segment—the research, development and sale of medical devices to assist or replace the pumping function of the failing heart. The Company’s chief operating decision maker (determined to be the Chief Executive Officer) does not manage any part of the Company separately, and the allocation of resources and assessment of performance are based on the Company’s consolidated operating results. International sales (sales outside the U.S. and primarily in Europe) accounted for 11%, 9% and 8% of total revenue during the fiscal years ended March 31, 2018, 2017 and 2016, respectively. As of March 31, 2018 and 2017, most of the Company’s long-lived assets are located in the U.S. except for $35.5 million and $23.2 million at March 31, 2018 and 2017, respectively, which are located primarily in Germany.

Quarterly Results of Operation

Quarterly Results of Operation	12 Months Ended
	Mar. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Quarterly Results of Operation	Note 14. Quarterly Results of Operation (Unaudited) The following is a summary of the Company’s unaudited quarterly results of operations for the fiscal years ending March 31, 2018 and 2017: Fiscal Year Ended March 31, 2018 1st Quarter 2nd Quarter 3rd Quarter 4th Quarter Total Year (in $000's) Revenue $ 132,468 $ 132,823 $ 154,022 $ 174,436 $ 593,749 Cost of revenue 21,862 21,627 24,994 30,098 98,581 Other operating expenses 77,528 79,470 84,262 96,771 338,031 Other income, net 714 758 888 940 3,300 Income before income taxes 33,792 32,484 45,654 48,507 160,437 Income tax provision (1)(2) (3,582 ) 7,981 32,208 11,660 48,267 Net income $ 37,374 $ 24,503 $ 13,446 $ 36,847 $ 112,170 Basic net income per share $ 0.85 $ 0.56 $ 0.30 $ 0.83 $ 2.54 Diluted net income per share $ 0.82 $ 0.54 $ 0.29 $ 0.80 $ 2.45 (1) On December 22, 2017, the Tax Cuts and Jobs Act, or Tax Reform Act, was enacted into law. This new law, among other items, reduces the U.S. federal statutory corporate income tax rate from 35% to 21% effective January 1, 2018. During the year ended March 31, 2018, the Company recorded tax expense adjustments for $21.4 million related to the revaluation of its deferred taxes due to a reduction of the U.S. federal statutory corporate income tax rate. (2) In the first quarter of fiscal 2018, the Company adopted Accounting Standards Update No. 2016-09, Improvements to Employee Share-Based Payment Accounting, which requires that all excess tax benefits and tax deficiencies related share-based compensation arrangements be recognized as income tax benefit or expense, instead of in stockholders’ equity as previous guidance required. The income tax benefit for the year ended March 31, 2018 included excess tax benefits of $31.0 million. These recognized excess tax benefits resulted from restricted stock units that vested or stock options that were exercised during the year ended March 31, 2018. Fiscal Year Ended March 31, 2017 1st Quarter 2nd Quarter 3rd Quarter 4th Quarter Total Year (in $000's) Revenue $ 102,995 $ 102,955 $ 114,674 $ 124,680 $ 445,304 Cost of revenue 15,070 17,309 18,987 19,261 70,627 Other operating expenses 66,692 71,138 70,284 76,425 284,539 Other income, net 192 228 423 362 1,205 Income before income taxes 21,425 14,736 25,826 29,356 91,343 Income tax provision 8,515 5,861 10,394 14,457 39,227 Net income $ 12,910 $ 8,875 $ 15,432 $ 14,899 $ 52,116 Basic net income per share $ 0.30 $ 0.21 $ 0.36 $ 0.34 $ 1.21 Diluted net income per share $ 0.29 $ 0.20 $ 0.34 $ 0.33 $ 1.17

Summary of Significant Accoun22

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
Principles of Consolidation	Principles of Consolidation The accompanying consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with generally accepted accounting principles of the United States of America, or 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 expenses during the reporting period. The Company bases its estimates on historical experience and various other factors believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying value of assets and liabilities that are not readily apparent from other sources. On an ongoing basis, the Company evaluates its estimates, including those related to revenue recognition, collectability of receivables, realizability of inventory, property and equipment, goodwill, intangible and other long-lived assets, accrued expenses, stock-based compensation, income taxes including deferred tax assets and liabilities, contingencies and litigation. Provisions for depreciation are based on their estimated useful lives using the straight-line method. Some of these estimates can be subjective and complex and, consequently, actual results may differ from these estimates under different assumptions or conditions.
Cash Equivalents and Marketable Securities	Cash Equivalents and Marketable Securities The Company classifies any marketable security with a maturity date of 90 days or less at the time of purchase as a cash equivalent. Cash equivalents are carried on the balance sheet at fair market value. The Company classifies any marketable security with a maturity date of greater than 90 days at the time of purchase as marketable securities and classifies marketable securities with a maturity date of greater than one year from the balance sheet date as long-term marketable securities. Marketable securities that the Company has the positive intent and ability to hold to maturity are reported at amortized cost and classified as held-to-maturity marketable securities. If the Company does not have the intent and ability to hold a marketable security to maturity, it reports the investment as available-for-sale marketable securities. The Company reports available-for-sale marketable securities at fair value, and includes unrealized gains and, to the extent deemed temporary, unrealized losses in stockholders’ equity. If any adjustment to fair value reflects a decline in the value of the investment, the Company considers available evidence to evaluate whether the decline is “other than temporary” and, if so, marks the marketable security to market through a charge reflected on the consolidated statements of operations.
Major Customers and Concentrations of Credit Risk	Major Customers and Concentrations of Credit Risk The Company primarily sells its products to hospitals and distributors. No customer accounted for more than 10% of total revenues in fiscal years ended March 31, 2018, 2017 or 2016. No individual customer had an accounts receivable balance greater than 10% of total accounts receivable at March 31, 2018 and 2017. Credit is extended based on an evaluation of a customer’s historical financial condition and generally collateral is not required. The Company’s history of credit losses has not been significant and the Company maintains an allowance for doubtful accounts based on its assessment of the collectability of accounts receivable. Accounts receivables are geographically dispersed, primarily throughout the U.S., as well as in Europe and other foreign countries where formal distributor agreements exist in certain countries. Financial instruments which potentially subject the Company to a concentration of credit risk consist of cash, cash equivalents, marketable securities, short and long-term marketable securities and accounts receivable. Management mitigates credit risk by limiting the investment type and maturity to securities that preserve capital, maintain liquidity and have a high credit quality.
Financial Instruments	Financial Instruments The Company’s financial instruments are comprised of cash and cash equivalents, marketable securities, accounts receivable, accounts payable and contingent consideration. The carrying amounts of accounts receivable and accounts payable are considered reasonable estimates of their fair value, due to the short maturity of these investments.
Inventories	Inventories Inventories are stated at the lower of cost or market. Cost is based on the first in, first out method. The Company regularly reviews inventory quantities on hand and writes down to its net realizable value any inventory that it believes to be impaired. Management considers forecast demand in relation to the inventory on hand, competitiveness of product offerings, market conditions and product life cycles when determining excess and obsolescence and net realizable value adjustments. Once inventory is written down and a new cost basis is established, it is not written back up if demand increases.
Property and Equipment	Property and Equipment Property and equipment is recorded at cost less accumulated depreciation. Land is carried at cost and is not depreciated. Depreciation is computed using the straight line method based on estimated useful lives of three to five years for machinery and equipment, computer software, and furniture and fixtures. Building and building improvements are depreciated using the straight-line method over estimated useful lives of seven to thirty-three years. Leasehold improvements are amortized using the straight-line method over the shorter of the lease term or the estimated useful lives of the related assets. Expenditures for maintenance and repairs are expensed as incurred. Upon retirement or other disposition of assets, the costs and related accumulated depreciation are eliminated from the accounts and the resulting gain or loss is reflected in operating expenses. Property and equipment is reviewed for impairment losses whenever events or changes in circumstances indicate the carrying amount may not be recoverable. An impairment loss would be recognized based on the amount by which the carrying value of the asset or asset group exceeds its fair value. Fair value is determined primarily using the estimated future cash flows associated with the asset or asset group under review discounted at a rate commensurate with the risk involved and other valuation techniques.
Leases	Leases Lease agreements are evaluated to determine whether they are capital or operating leases in accordance with Financial Accounting Standards Board, or ASC, 840, Leases Rent expense for operating leases, which may include free rent or fixed escalation amounts in addition to minimum lease payments, is recognized on a straight-line basis over the duration of each lease term.
Goodwill	Goodwill Goodwill is recorded when consideration for an acquisition exceeds the fair value of the net tangible and intangible assets acquired. Goodwill is not amortized, instead the Company evaluates goodwill for impairment at least annually at October 31, as well as whenever events or changes in circumstances suggest that the carrying amount may not be recoverable. Goodwill impairment assessments are performed at the reporting unit level. The goodwill test involves a two-step process. The first step is a comparison of the reporting unit’s fair value to its carrying value. If the reporting unit’s fair value exceeds its carrying value, no further procedures are required. However, if the reporting unit’s fair value is less than the carrying value, an impairment of goodwill may exist, requiring a second step to measure the amount of impairment loss. If the implied fair value of goodwill is less than the recorded goodwill, an impairment charge is recorded for the difference. In applying the goodwill impairment test, the Company may assess qualitative factors to determine whether it is more likely than not that the fair value of the reporting unit is less than its carrying value. Qualitative factors may include, but are not limited to, macroeconomic conditions, industry conditions, the competitive environment, changes in the market for our products and services, regulatory and political developments, cost factors, and entity specific factors such as strategies and overall financial performance. If, after assessing these qualitative factors, the Company determines it is not more likely than not that the fair value of a reporting unit is less than its carrying value, then performing the two-step impairment test is unnecessary. The goodwill impairment test is performed at the reporting unit level by comparing the reporting unit’s carrying value, including goodwill, to the fair value of the reporting unit. The Company estimates the fair value of its single reporting unit using a combination of the income approach and the market approach. The income approach incorporates the use of a discounted cash flow method in which the estimated future cash flows and terminal values for the reporting unit is discounted to a present value using an appropriate discount rate. Cash flow projections are based on management’s estimates of economic and market conditions which drive key assumptions of revenue growth rates, operating margins, cash flows, capital expenditures and working capital requirements. The discount rate is based on the specific risk characteristics of the reporting unit and its underlying forecast. The market approach estimates fair value by comparing publicly traded companies with similar operating and investment characteristics as the reporting unit. The fair values determined by the market approach and income approach, are weighted to determine the fair value for the reporting unit based primarily on the similarity of the operating and investment characteristics of the reporting unit to the comparable publicly traded companies used in the market approach.
In-Process Research and Development	In-Process Research and Development In-process research and development, or IPR&D, assets are considered to be indefinite-lived until the completion or abandonment of the associated research and development projects. IPR&D assets represent the fair value assigned to technologies that are acquired, which at the time of acquisition have not reached technological feasibility and have no alternative future use. During the period that the IPR&D assets are considered indefinite-lived, they are tested for impairment on an annual basis on October 31, or more frequently if the Company becomes aware of any events occurring or changes in circumstances that indicate that the fair value of the IPR&D assets are less than their carrying values. If and when development is complete, which generally occurs upon regulatory approval and the Company is able to commercialize products associated with the IPR&D assets, these assets are then deemed definite-lived and are amortized based on their estimated useful lives at that point in time. If development is terminated or abandoned, the Company may have a full or partial impairment charge related to the IPR&D assets, calculated as the excess of carrying value of the IPR&D assets over fair value.
Contingent Consideration	Contingent Consideration Contingent consideration represents potential milestones that the Company could pay additional consideration for a business acquisition and is recorded as a liability and is measured at fair value using a combination of 1) an income approach, based on various revenue and cost assumptions and applying a probability to each outcome and 2) a Monte-Carlo valuation model that simulates outcomes based on management estimates. With the income approach, p robabilities were applied to each potential scenario and the resulting values were discounted using a rate that considers the weighted average cost of capital, the related projections, and the overall business. The Monte-Carlo valuation model simulates estimated future revenues during the earn out-period using management's best estimates.
Accrued Expenses	Accrued Expenses As part of the process of preparing its financial statements, the Company is required to estimate accrued expenses. This process includes identifying services that third parties have performed and estimating the level of service performed and the associated cost incurred on these services as of each balance sheet date in its financial statements. Examples of estimated accrued expenses include contract service fees, such as amounts due to clinical research organizations, investigators in conjunction with clinical trials, professional service fees, such as attorneys and accountants, and third party expenses relating to marketing efforts associated with commercialization of the Company’s product and product candidates. Accrued expenses also include estimates for payroll costs, such as bonuses and commissions. In the event that the Company does not identify certain costs that have been incurred or it under or over-estimates the level of services or the costs of such services, reported expenses for a reporting period could be overstated or understated. The dates in which certain services commence and end, the level of services performed on or before a given date and the cost of services is often subject to the Company’s judgment. The Company makes these judgments and estimates based upon known facts and circumstances.
Revenue Recognition	Revenue Recognition The Company recognizes revenue when evidence of an arrangement exists, title has passed or services have been rendered, the selling price is fixed or determinable and collectability is reasonably assured. Revenue from product sales to customers is recognized when delivery has occurred. All costs related to product sales are recognized at time of delivery. The Company does not provide for rights of return to customers on product sales and therefore does not record a provision for returns. Maintenance and service support contract revenues are included in revenue and are recognized ratably over the term of the service contracts. Revenue is recognized as earned in limited instances where the Company rents its console medical devices on a month-to-month basis or for a longer specified period of time to customers. In May 2014, the FASB, issued ASU 2014-09, Revenue from Contracts with Customers to provide updated guidance on revenue recognition. This new standard will replace most of the existing revenue recognition guidance in U.S. GAAP when it becomes effective and permits the use of either the retrospective or cumulative effect transition method. ASU 2014-09 requires a company to recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods or services. In doing so, companies may need to use more judgment and make more estimates than under the current accounting guidance. These may include identifying performance obligations in the contract, estimating the amount of variable consideration to include in the transaction price and allocating the transaction price to each separate performance obligation. The guidance also requires expanded disclosures relating to the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. Additionally, qualitative and quantitative disclosures are required about customer contracts, significant judgments and changes in judgments, and assets recognized from the costs to obtain or fulfill a contract. The Company is implementing the necessary changes to its revenue recognition accounting policies and controls to support recognition and disclosure under the new standard. The Company will adopt ASU 2014-09 during the first quarter of fiscal 2019.
Product Warranty	Product Warranty The Company generally provides a one-year warranty for certain products sold in which estimated contractual warranty obligations are recorded as an expense at the time of shipment. The Company’s products are subject to regulatory and quality standards. Future warranty costs are estimated based on historical product performance rates and related costs to repair given products. The accounting estimate related to product warranty expense involves judgment in determining future estimated warranty costs. Should actual performance rates or repair costs differ from estimates, revisions to the estimated warranty liability would be required.
Accumulated Other Comprehensive Income (Loss)	Accumulated Other Comprehensive Income (Loss) Comprehensive income (loss) is comprised of net income, plus all changes in equity of a business enterprise during a period from transactions and other events and circumstances from non-owner sources, including any foreign currency translation adjustments. These changes in equity are recorded as adjustments to accumulated other comprehensive income (loss) in the Company’s consolidated balance sheet. The components of accumulated other comprehensive income (loss) consist of foreign currency translation adjustments and changes in unrealized gains (losses) on marketable securities. There were no reclassifications out of accumulated other comprehensive income (loss) during the fiscal years ended March 31, 2018, 2017 and 2016.
Translation of Foreign Currencies	Translation of Foreign Currencies The functional currency of the Company’s foreign subsidiaries is their local currency. The assets and liabilities of the Company’s foreign subsidiaries are translated into U.S. dollars at exchange rates in effect at the balance sheet date. Income and expense items in the Company’s consolidated statement of operations are translated at the average exchange rates prevailing during the period. The cumulative translation effect for subsidiaries using a functional currency other than the U.S. dollar is included in accumulated other comprehensive income (loss) as a separate component of stockholders’ equity. The Company’s intercompany accounts are denominated in the functional currency of the foreign subsidiary. Gains and losses resulting from the remeasurement of intercompany receivables that the Company considers to be of a long-term investment nature are recorded in accumulated other comprehensive income or loss as a separate component of stockholders’ equity, while gains and losses resulting from the remeasurement of intercompany receivables from those foreign subsidiaries for which the Company anticipates settlement in the foreseeable future are recorded in the consolidated statement of operations. The net foreign currency translation gains and losses recorded in the consolidated statements of operations for the fiscal years ended March 31, 2018, 2017 and 2016 were not significant.
Net Income Per Share	Net Income Per Share Basic net income per share is computed by dividing net income by the weighted average number of common shares outstanding during the fiscal year. Diluted net income per share is computed using the treasury stock method by dividing net income by the weighted average number of dilutive common shares outstanding during the fiscal year. Diluted shares outstanding is calculated by adding to the weighted average shares outstanding any potential dilutive securities outstanding for the fiscal year. Potential dilutive securities include stock options, restricted stock units, performance-based restricted stock units and shares to be purchased under the Company’s employee stock purchase plan. In fiscal years when a net loss is reported, all common stock equivalents are excluded from the calculation because they would have an anti-dilutive effect, meaning the loss per share would be reduced. Therefore, in periods when a loss is reported basic and dilutive loss per share are the same. For the fiscal years ended March 31, 2018, 2017 and 2016, the Company’s basic and diluted net income per share were as follows (in thousands, except per share data): Fiscal Years Ended March 31, 2018 2017 2016 Basic Net Income Per Share Net income $ 112,170 $ 52,116 $ 38,147 Weighted average shares used in computing basic net income per share 44,153 43,238 42,204 Net income per share - basic $ 2.54 $ 1.21 $ 0.90 Fiscal Years Ended March 31, 2018 2017 2016 Diluted Net Income Per Share Net income $ 112,170 $ 52,116 $ 38,147 Weighted average shares used in computing basic net income per share 44,153 43,238 42,204 Effect of dilutive securities 1,696 1,420 2,691 Weighted average shares used in computing diluted net income per share 45,849 44,658 44,895 Net income per share - diluted $ 2.45 $ 1.17 $ 0.85 For the fiscal years ended March 31, 2018, 2017 and 2016, approximately 155,000, 24,000 and 62,000 shares of common stock underlying outstanding securities primarily related to out-of-the-money stock options and performance-based awards where milestones were not met were not included in the computation of diluted earnings per share because their inclusion would be anti-dilutive.
Stock-Based Compensation	Stock-Based Compensation The Company’s stock-based compensation cost is measured at the grant date based on the fair value of the award and is recognized as an expense over the requisite service period. The fair value of stock option grants is estimated using the Black-Scholes option pricing model. Use of the valuation model requires management to make certain assumptions with respect to selected model inputs. The risk-free interest rate is based on the U.S. Treasury yield curve in effect at the time of grant for a term consistent with the expected life of the stock options. Volatility assumptions are calculated based on historical volatility of the Company’s stock. The Company estimates the expected term of options based on historical exercise experience and estimates of future exercises of unexercised options. In addition, an expected dividend yield of zero is used in the option valuation model because the Company does not pay cash dividends and does not expect to pay any cash dividends in the foreseeable future. Forfeitures are recorded as they occur instead of estimating forfeitures that are expected to occur. An accounting policy change was made by the Company related to the recording of forfeitures during the quarter ended June 30, 2017 as a result of the adoption of ASU 2016-09, “Compensation – Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting” For awards with service conditions only, the Company recognizes stock-based compensation expense on a straight-line basis over the requisite service period. For awards with service, performance and market-based conditions, the Company recognizes stock-based compensation expense using the graded vesting method over the requisite service period. Estimates of stock-based compensation expense for an award with performance conditions are based on the probable outcome of the performance conditions. The cumulative effect of changes in the probability outcomes are recorded in the period in which the changes occur. For awards with market-based conditions, the Company uses a Monte Carlo simulation model to estimate that the grant-date fair value. The fair value related to market-based awards is recorded as stock-based compensation expense over the vesting period regardless of whether the market condition is achieved or not.
Income Taxes	Income Taxes The Company’s provision for income taxes is comprised of a current and deferred provision. The current income tax provision is calculated as the estimated taxes payable or refundable on income tax returns for the current fiscal year. The deferred income tax provision is calculated for the estimated future income tax effects attributable to temporary differences and carryforwards using expected tax rates in effect in the years during which the temporary differences are expected to reverse. Deferred income taxes are recognized for the tax consequences in future years as the differences between the tax bases of assets and liabilities and their financial reporting amounts at each fiscal year end based on enacted tax laws and statutory tax rates applicable to the periods in which the differences are expected to impact taxable income. The Company regularly assesses its ability to realize its deferred tax assets. Assessing the realization of deferred tax assets requires significant management judgment. Valuation allowances are established when necessary to reduce net deferred tax assets to the amount that is more likely than not to be realized. The Company recognizes and measures uncertain tax positions using a two-step approach. The first step is to evaluate the tax position for recognition by determining if, based on the technical merits, it is more likely than not that the position will be sustained upon audit, including resolution of related appeals or litigation processes, if any. The second step is to measure the tax benefit at the largest amount that is more likely than not of being realized upon ultimate settlement. The Company reevaluates these uncertain tax positions on an ongoing basis, when applicable. This evaluation is based on factors including, but not limited to, changes in facts or circumstances, new information and technical insights, and changes in tax laws. Any changes in these factors could result in the recognition of a tax benefit or an additional charge to the tax provision. Please refer to “Note 10. Income Taxes” for further information related to the Tax Reform Act (defined below) and its impact on the Company’s financial statements. When applicable, the Company accrues for the effects of uncertain tax positions and the related potential penalties and interest through income tax expense.
New Accounting Pronouncements Adopted	New Accounting Pronouncements Adopted Effective April 1, 2017, the Company adopted the Financial Accounting Standards Board, FASB, standard update ASU 2016-09, “ Compensation – Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting, The following table summarizes the most significant impacts of ASU 2016-09 for the year ended March 31, 2018: Description of Change: Impact of Change Upon Adoption on April 1, 2017 and for the Year Ended March 31, 2018: Adoption Method: The new standard eliminates the requirement that excess tax benefits be realized through a reduction in income taxes payable before a company can recognize them in the statement of operations. As a result, on April 1, 2017, the Company recorded a cumulative-effect adjustment to increase retained earnings and deferred tax assets by $76.4 million for excess tax benefits not previously recognized. Modified-retrospective (required) Excess tax benefits related to restricted stock unit vestings or stock option exercises are recorded through the statement of operations. The income tax benefit for the year ended March 31, 2018 included excess tax benefits of $31.0 million. These recognized excess tax benefits resulted from restricted stock units that vested or stock options that were exercised during the year ended March 31, 2018. Prospective (required) Excess tax benefits related to restricted stock unit vestings or stock option exercises are classified as operating cash flows instead of financing cash flows. Increase in cash flow from operating activities and decrease in cash flow from financing activities by approximately $31.0 million for the year ended March 31, 2018. The statement of cash flows for the prior period has not been adjusted. Prospective (elected) Calculation of diluted weighted average shares outstanding under the treasury method no longer assume that tax benefits related to stock-based awards are used to repurchase common stock. The Company excluded the related tax benefits when applying the treasury stock method for computing diluted shares outstanding on a prospective basis as required by ASU 2016-09. Prospective (required) An accounting policy election can be made to reduce stock-based compensation expense for forfeitures as they occur instead of estimating forfeitures that are expected to occur. The Company made an accounting policy election to account for forfeitures as they occur with the change applied on a modified retrospective basis with a cumulative effect adjustment on April 1, 2017 to increase additional paid-in capital by $1.8 million, increase deferred tax assets by $0.7 million and decrease retained earnings by $1.1 million. The Company elected to make this accounting policy change to simplify the accounting for stock-based compensation and believes this method provides a more accurate reflection of periodic stock based compensation cost. Prior to the adoption of this accounting standard, the Company estimated at grant the likelihood that the award would ultimately vest, and revised the estimate, if necessary, in future periods if the actual forfeiture rate differed. Modified-retrospective (elected) Cash payments to tax authorities for shares withheld to meet employee tax withholding requirements on restricted stock units are classified as financing cash flow instead of operating cash flow. No change since the Company has historically presented these amounts as a financing activity. Prior to ASU 2016-09, U.S. GAAP has not specified how these types of transactions should be classified in the statement of cash flows. N/A See table below for the changes in beginning stockholders’ equity as a result of this implementation. Common Stock Treasury Stock Number of shares Par value Number of shares Amount Additional Paid in Capital Accumulated Deficit Accumulated Other Comprehensive Income (Loss) Total Stockholders' Equity Balance, March 31, 2017 43,673,286 $ 437 1,575,995 $ (46,763 ) $ 565,962 $ (46,959 ) $ (20,606 ) $ 452,071 Cumulative effect of adoption of new accounting standard 1,835 75,246 77,081 Balance, April 1, 2017 43,673,286 $ 437 1,575,995 $ (46,763 ) $ 567,797 $ 28,287 $ (20,606 ) $ 529,152
Recent Accounting Pronouncements	Recent Accounting Pronouncements In May 2014, the FASB, issued ASU 2014-09, Revenue from Contracts with Customers The Company established an implementation team to assist with its assessment of the impact of the new revenue guidance on its operations, consolidated financial statements and related disclosures. The Company’s assessment has included performing analysis for each revenue stream identified, assessing the potential differences in recognition and measurement that may result from adopting this standard and assessing whether the Company meets certain practical expedients. Based on the results of the assessment, the adoption of this standard will not have a material impact on the timing or amount of revenue recognized upon adoption and there is no significant cumulative prior period adjustment to be recorded to the opening balance of retained earnings upon adoption. The Company also anticipates changes to its disclosures to comply with the new disclosure requirements. The Company is implementing the necessary changes to its revenue recognition accounting policies and controls to support recognition and disclosure under the new standard. In January 2016, the FASB issued ASU 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities In February 2016, the FASB issued ASU 2016-02, Leases

Summary of Significant Accoun23

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
Schedule of Earnings Per Share Basic And Diluted	Fiscal Years Ended March 31, 2018 2017 2016 Basic Net Income Per Share Net income $ 112,170 $ 52,116 $ 38,147 Weighted average shares used in computing basic net income per share 44,153 43,238 42,204 Net income per share - basic $ 2.54 $ 1.21 $ 0.90 Fiscal Years Ended March 31, 2018 2017 2016 Diluted Net Income Per Share Net income $ 112,170 $ 52,116 $ 38,147 Weighted average shares used in computing basic net income per share 44,153 43,238 42,204 Effect of dilutive securities 1,696 1,420 2,691 Weighted average shares used in computing diluted net income per share 45,849 44,658 44,895 Net income per share - diluted $ 2.45 $ 1.17 $ 0.85
Schedule of Changes in Beginning Stockholders’ Equity	See table below for the changes in beginning stockholders’ equity as a result of this implementation. Common Stock Treasury Stock Number of shares Par value Number of shares Amount Additional Paid in Capital Accumulated Deficit Accumulated Other Comprehensive Income (Loss) Total Stockholders' Equity Balance, March 31, 2017 43,673,286 $ 437 1,575,995 $ (46,763 ) $ 565,962 $ (46,959 ) $ (20,606 ) $ 452,071 Cumulative effect of adoption of new accounting standard 1,835 75,246 77,081 Balance, April 1, 2017 43,673,286 $ 437 1,575,995 $ (46,763 ) $ 567,797 $ 28,287 $ (20,606 ) $ 529,152

Cash Equivalents, Marketable 24

Cash Equivalents, Marketable Securities and Fair Value Measurements (Tables)	12 Months Ended
	Mar. 31, 2018
Fair Value Disclosures [Abstract]
Cash Equivalents and Marketable Securities by Balance Sheet Classification	The Company’s cash equivalents and marketable securities at March 31, 2018 and 2017 are classified on the balance sheet as follows: March 31, 2018 March 31, 2017 (in $000's) Cash equivalents (within 90 days at the time of purchase to maturity) $ 22,595 $ 23,975 Short-term marketable securities (within one year to maturity) 319,274 190,908 Long-term marketable securities (one to two years to maturity) 37,502 47,143 $ 379,371 $ 262,026
Cash Equivalents and Marketable Securities	The Company’s cash equivalents and marketable securities at March 31, 2018 and 2017 are invested in the following: Amortized Gross Unrealized Gross Unrealized Fair Market Cost Gains Losses Value (in $000's) March 31, 2018: Money market funds $ 5,845 $ — $ — $ 5,845 Repurchase agreements 16,750 — — 16,750 Short-term U.S. Treasury mutual fund securities 18,132 — (29 ) 18,103 Short-term government-backed securities 212,255 3 (538 ) 211,720 Short-term corporate debt securities 52,737 — (161 ) 52,576 Short-term commercial paper 36,936 2 (63 ) 36,875 Long-term U.S. Treasury mutual fund securities 10,953 — (16 ) 10,937 Long-term government-backed securities 24,798 1 (12 ) 24,787 Long-term corporate debt securities 1,777 1 — 1,778 $ 380,183 $ 7 $ (819 ) $ 379,371 Amortized Gross Unrealized Gross Unrealized Fair Market Cost Gains Losses Value (in $000's) March 31, 2017: Money market funds $ 11,975 $ — $ — $ 11,975 Repurchase agreements 12,000 — — 12,000 Short-term U.S. Treasury mutual fund securities 45,199 — (13 ) 45,186 Short-term government-backed securities 90,199 1 (87 ) 90,113 Short-term corporate debt securities 13,161 — (6 ) 13,155 Short-term commercial paper 42,304 — (25 ) 42,279 Long-term U.S. Treasury mutual fund securities 1,998 — (3 ) 1,995 Long-term government-backed securities 43,484 5 (18 ) 43,471 Long-term corporate debt securities 1,853 — (1 ) 1,852 $ 262,173 $ 6 $ (153 ) $ 262,026
Financial Instruments Measured at Fair Value	The following table presents the Company’s fair value hierarchy for its financial instruments measured at fair value as of March 31, 2018 and 2017: Level 1 Level 2 Level 3 Total March 31, 2018: (in $000's) Assets Money market funds $ 5,845 $ — $ — $ 5,845 Repurchase agreements — 16,750 — 16,750 Short-term U.S. Treasury mutual fund securities — 18,103 — 18,103 Short-term government-backed securities — 211,720 — 211,720 Short-term corporate debt securities — 52,576 — 52,576 Short-term commercial paper — 36,875 — 36,875 Long-term U.S. Treasury mutual fund securities — 10,937 — 10,937 Long-term government-backed securities — 24,787 — 24,787 Long-term corporate debt securities — 1,778 — 1,778 Liabilities Contingent consideration — — 10,490 10,490 Level 1 Level 2 Level 3 Total March 31, 2017: (in $000's) Assets Money market funds $ 11,975 $ — $ — $ 11,975 Repurchase agreements — 12,000 — 12,000 Short-term U.S. Treasury mutual fund securities — 45,186 — 45,186 Short-term government-backed securities — 90,113 — 90,113 Short-term corporate debt securities — 13,155 — 13,155 Short-term commercial paper — 42,279 — 42,279 Long-term U.S. Treasury mutual fund securities — 1,995 — 1,995 Long-term government-backed securities — 43,471 — 43,471 Long-term corporate debt securities — 1,852 — 1,852 Liabilities Contingent consideration — — 9,153 9,153
Valuation Method Used to Calculate Level 3 Liabilities Measured at Estimated Fair Value of Contingent Consideration Related to Acquisition	This liability is reported as Level 3 as the estimated fair value of the contingent consideration related to the acquisition of ECP requires significant management judgment or estimation and is calculated using the following valuation methods: Fair Value at March 31, 2018 (in $000's) Valuation Methodology Significant Unobservable Input Weighted Average (range, if applicable) Clinical and regulatory milestone $ 5,631 Probability weighted income approach Projected fiscal year of milestone payments 2019 to 2022 Discount rate 3.2% to 3.8% Probability of occurrence Probability adjusted level of 40% for the base case scenario and 12% to 30% for various upside and downside scenarios Revenue-based milestone 4,859 Monte Carlo simulation model Projected fiscal year of milestone payments 2023 to 2035 Discount rate 18% Expected volatility for forecasted revenues 50% Probability of payment (risk-neutral) 78.5% $ 10,490
Change in Fair Value of Contingent Consideration as Determined by Level 3 Inputs	The following table summarizes the change in fair value, as determined by Level 3 inputs, of the contingent consideration for the fiscal years ended March 31, 2018, 2017 and 2016: Fiscal Years Ended March 31, 2018 2017 2016 (in $000's) Level 3 liabilities, beginning balance $ 9,153 $ 7,563 $ 6,510 Additions — — — Payments — — — Change in fair value 1,337 1,590 1,053 Level 3 liabilities, ending balance $ 10,490 $ 9,153 $ 7,563

Accounts Receivable (Tables)

Accounts Receivable (Tables)	12 Months Ended
	Mar. 31, 2018
Receivables [Abstract]
Components of Accounts Receivable	The components of accounts receivable are as follows: March 31, 2018 March 31, 2017 (in $000's) Trade receivables $ 70,330 $ 54,337 Allowance for doubtful accounts (320 ) (282 ) $ 70,010 $ 54,055
Summary of Allowance for Doubtful Accounts Receivable	The following table summarizes activity in the Company's allowance for doubtful accounts: Fiscal Years Ended March 31, 2018 2017 2016 (in $000's) Balance at beginning of year $ 282 $ 124 $ 177 Additions 38 159 42 Write-offs — (1 ) (95 ) Balance at end of year $ 320 $ 282 $ 124

Inventories (Tables)

Inventories (Tables)	12 Months Ended
	Mar. 31, 2018
Inventory Disclosure [Abstract]
Components of Inventories	The components of inventories are as follows: March 31, 2018 March 31, 2017 (in $000's) Raw materials and supplies $ 16,481 $ 9,784 Work-in-progress 23,179 16,504 Finished goods 10,544 8,643 $ 50,204 $ 34,931

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
	Mar. 31, 2018
Property Plant And Equipment [Abstract]
Components of Property and Equipment	The components of property and equipment are as follows: March 31, 2018 March 31, 2017 (in $000's) Land $ 7,680 $ 4,046 Building and building improvements 63,700 10,900 Capital lease asset — 16,784 Leasehold improvements 2,905 34,854 Machinery and equipment 42,787 27,989 Furniture and fixtures 8,104 3,899 Construction in progress 19,850 9,257 Total cost 145,026 107,729 Less accumulated depreciation (27,859 ) (19,952 ) $ 117,167 $ 87,777

Goodwill and In-Process Resea28

Goodwill and In-Process Research and Development (Tables)	12 Months Ended
	Mar. 31, 2018
Goodwill And Intangible Assets Disclosure [Abstract]
Goodwill Activity	The goodwill activity is as follows: (in $000's) Balance at March 31, 2016 $ 33,003 Foreign currency translation impact (1,958 ) Balance at March 31, 2017 $ 31,045 Foreign currency translation impact 4,763 Balance at March 31, 2018 $ 35,808
Carrying value of In-Process Research and Development	The carrying value of the Company’s IPR&D assets and the change in the balance for the fiscal years ended March 31, 2018 and 2017 is as follows: (in $000's) Balance at March 31, 2016 $ 15,396 Foreign currency translation impact (914 ) Balance at March 31, 2017 $ 14,482 Foreign currency translation impact 2,223 Balance at March 31, 2018 $ 16,705

Stock Award Plans and Stock-B29

Stock Award Plans and Stock-Based Compensation (Tables)	12 Months Ended
	Mar. 31, 2018
Stock-Based Compensation Recognized	The following table summarizes stock-based compensation expense by financial statement line item in the Company’s consolidated statements of operations for the fiscal years ended March 31, 2018, 2017 and 2016: Fiscal Years Ended March 31, 2018 2017 2016 (in $000's) Cost of revenue $ 1,721 $ 1,061 $ 895 Research and development 5,895 6,050 3,950 Selling, general and administrative 32,737 25,755 24,208 $ 40,353 $ 32,866 $ 29,053
Components of Stock-Based Compensation	The components of stock-based compensation for the fiscal years ended March 31, 2018, 2017 and 2016 were as follows: Fiscal Years Ended March 31, 2018 2017 2016 (in $000's) Restricted stock units $ 34,559 $ 26,570 $ 23,708 Stock options 5,202 5,829 4,866 Employee stock purchase plan 592 467 479 $ 40,353 $ 32,866 $ 29,053
Summary of Stock Option Activity	The following table summarized stock option activity for the fiscal year ended March 31, 2018: Weighted Weighted Average Aggregate Average Remaining Intrinsic Options Exercise Contractual Value (in thousands) Price Term (years) (in thousands) Outstanding at beginning of period 1,646 $ 32.09 5.46 Granted 155 143.52 Exercised (460 ) 20.23 Cancelled and expired (59 ) 98.21 Outstanding at end of period 1,282 $ 46.81 5.31 $ 313,158 Exercisable at end of period 965 $ 24.88 4.29 $ 256,891 Options vested and expected to vest at end of period 1,259 $ 46.18 5.27 $ 308,252
Summary of Weighted Average Grant-Date Fair Values And Weighted Average Assumptions Used to Calculate Fair Value of Options Granted	The weighted average grant-date fair values and weighted average assumptions used in the calculation of fair value of options granted during the fiscal years ended March 31, 2018, 2017 and 2016 was as follows: Fiscal Years Ended March 31, 2018 2017 2016 Valuation assumptions: Weighted average grant-date fair value $ 52.34 $ 42.40 $ 29.57 Risk-free interest rate 1.87 % 1.41 % 1.55 % Expected option life (years) 4.07 4.14 4.15 Expected volatility 43.5 % 48.9 % 49.7 %
Summary of Restricted Stock Units Activity	The following table summarizes restricted stock unit activity for the fiscal year ended March 31, 2018: Number of Shares Weighted Average Grant Date Fair Value (in thousands) (per share) Restricted stock units at beginning of period 1,056 $ 80.50 Granted 296 $ 137.40 Vested (372 ) $ 53.40 Forfeited (100 ) $ 98.47 Restricted stock units at end of period 880 $ 109.01
Restricted Stock Units
Monte Carlo Simulation Model to Estimate Grant-Date Fair Value of Restricted Stock Units	The table below sets forth the assumptions used to value the market-based awards and the estimated grant-date fair value: June 2015 Awards November 2016 Awards Risk-free interest rate 1.10 % 0.90 % Dividend yield 0 % 0 % Remaining performance period (years) 0.21 0.21 Expected volatility 47.2 % 50.6 % Estimated grant date fair value (per share) $ 93.49 - 107.10 $ 62.55 Target performance (number of shares) 107,660 41,526

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Mar. 31, 2018
Income Tax Disclosure [Abstract]
Income before Income Taxes	The components of the Company’s income tax provision for the fiscal years ended March 31, 2018, 2017 and 2016 are as follows: 2018 2017 2016 (in $000's) Income before provision for income taxes: United States $ 134,006 $ 78,172 $ 54,406 Foreign 26,431 13,170 11,432 Income before income taxes $ 160,437 $ 91,342 $ 65,838 Current tax expense: Federal $ 752 $ 7,313 $ 1,690 State 1,491 5,045 2,113 Foreign 3,400 1,066 1,592 5,643 13,424 5,395 Deferred tax expense (benefit): Federal 38,848 23,008 18,769 State (1,014 ) (349 ) 1,284 Foreign 4,790 3,144 2,243 42,624 25,803 22,296 Total income tax provision $ 48,267 $ 39,227 $ 27,691
Components of Income Tax Provision (Benefit)	The components of the Company’s income tax provision for the fiscal years ended March 31, 2018, 2017 and 2016 are as follows: 2018 2017 2016 (in $000's) Income before provision for income taxes: United States $ 134,006 $ 78,172 $ 54,406 Foreign 26,431 13,170 11,432 Income before income taxes $ 160,437 $ 91,342 $ 65,838 Current tax expense: Federal $ 752 $ 7,313 $ 1,690 State 1,491 5,045 2,113 Foreign 3,400 1,066 1,592 5,643 13,424 5,395 Deferred tax expense (benefit): Federal 38,848 23,008 18,769 State (1,014 ) (349 ) 1,284 Foreign 4,790 3,144 2,243 42,624 25,803 22,296 Total income tax provision $ 48,267 $ 39,227 $ 27,691
Components of Net Deferred Taxes	The components of the Company’s net deferred taxes were as follows: March 31, 2018 2017 (in $000's) Deferred tax assets Non-operating loss and tax credit carryforwards $ 48,724 $ 8,814 Stock-based compensation 13,271 16,560 Nondeductible reserves and accruals 8,290 10,303 Foreign non-operating loss carryforwards 9,598 13,634 Deferred revenue 3,770 4,308 Depreciation and amortization 826 2,135 Other, net 822 1,308 85,301 57,062 Deferred tax liabilities Goodwill (6,787 ) (9,444 ) In-process research and development (5,045 ) (4,374 ) Depreciation (1,011 ) — Domestic deferred tax liability on foreign non-operating loss carryforwards (963 ) (6,836 ) (13,806 ) (20,654 ) Net deferred tax assets 71,495 36,408 Valuation allowance (1,652 ) (2,468 ) Net deferred tax assets $ 69,843 $ 33,940 Reported as: Long-term deferred tax assets, net $ 70,746 $ 34,723 Long-term deferred tax liabilities (903 ) (783 ) Net deferred tax assets $ 69,843 $ 33,940
Differences Between Federal Statutory Income Tax Rate and Effective Tax Rates	A reconciliation of the federal statutory income tax rate to the Company’s effective income tax rate is as follows for the fiscal years ended March 31, 2018, 2017, and 2016: 2018 2017 2016 Statutory income tax rate 31.5 % 35.0 % 35.0 % (Decrease) increase resulting from: Change in valuation allowance 0.5 0.2 0.7 Credits (4.9 ) (3.3 ) (4.1 ) Foreign taxes 2.2 2.0 2.5 State taxes, net 2.0 3.8 3.7 Permanent differences 2.4 3.3 3.0 Stock-based compensation (17.2 ) 0.2 0.3 Rate differential on foreign operations — 0.1 — Effect of the Tax Reform Act on net deferred tax assets 13.0 — — Other 0.6 1.7 1.0 Effective tax rate 30.1 % 43.0 % 42.1 %
Changes in Valuation Allowance for Deferred Tax Assets	Changes in the valuation allowance for deferred tax assets during the fiscal years ended March 31, 2018, 2017 and 2016 were as follows: 2018 2017 2016 (in $000's) Balance at beginning of year $ 2,468 $ 2,418 $ 2,912 Increases 325 50 677 Decreases (1,141 ) — (1,171 ) Balance at end of year $ 1,652 $ 2,468 $ 2,418

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Mar. 31, 2018
Commitments And Contingencies Disclosure [Abstract]
Future Minimum Lease Payments Under Non-Cancelable Leases	Future minimum lease payments under non-cancelable leases as of March 31, 2018 are approximately as follows: Fiscal Years Ending March 31, Operating Leases (in $000s) 2019 $ 2,078 2020 1,888 2021 1,901 2022 1,408 2023 891 Thereafter 1,923 Total minimum lease payments $ 10,089

Accrued Expenses (Tables)

Accrued Expenses (Tables)	12 Months Ended
	Mar. 31, 2018
Payables And Accruals [Abstract]
Accrued Expenses	Accrued expenses consisted of the following: March 31, 2018 March 31, 2017 (in $000's) Employee compensation $ 30,330 $ 23,290 Sales and income taxes 4,562 3,180 Research and development 3,162 2,349 Marketing 2,305 1,827 Professional, legal and accounting fees 1,870 2,019 Warranty 1,081 717 Accrued capital expenditures 250 2,300 Other 2,587 2,021 $ 46,147 $ 37,703

Quarterly Results of Operation

Quarterly Results of Operation (Tables)	12 Months Ended
	Mar. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Summary of Unaudited Quarterly Results of Operations	The following is a summary of the Company’s unaudited quarterly results of operations for the fiscal years ending March 31, 2018 and 2017: Fiscal Year Ended March 31, 2018 1st Quarter 2nd Quarter 3rd Quarter 4th Quarter Total Year (in $000's) Revenue $ 132,468 $ 132,823 $ 154,022 $ 174,436 $ 593,749 Cost of revenue 21,862 21,627 24,994 30,098 98,581 Other operating expenses 77,528 79,470 84,262 96,771 338,031 Other income, net 714 758 888 940 3,300 Income before income taxes 33,792 32,484 45,654 48,507 160,437 Income tax provision (1)(2) (3,582 ) 7,981 32,208 11,660 48,267 Net income $ 37,374 $ 24,503 $ 13,446 $ 36,847 $ 112,170 Basic net income per share $ 0.85 $ 0.56 $ 0.30 $ 0.83 $ 2.54 Diluted net income per share $ 0.82 $ 0.54 $ 0.29 $ 0.80 $ 2.45 (1) On December 22, 2017, the Tax Cuts and Jobs Act, or Tax Reform Act, was enacted into law. This new law, among other items, reduces the U.S. federal statutory corporate income tax rate from 35% to 21% effective January 1, 2018. During the year ended March 31, 2018, the Company recorded tax expense adjustments for $21.4 million related to the revaluation of its deferred taxes due to a reduction of the U.S. federal statutory corporate income tax rate. (2) In the first quarter of fiscal 2018, the Company adopted Accounting Standards Update No. 2016-09, Improvements to Employee Share-Based Payment Accounting, which requires that all excess tax benefits and tax deficiencies related share-based compensation arrangements be recognized as income tax benefit or expense, instead of in stockholders’ equity as previous guidance required. The income tax benefit for the year ended March 31, 2018 included excess tax benefits of $31.0 million. These recognized excess tax benefits resulted from restricted stock units that vested or stock options that were exercised during the year ended March 31, 2018. Fiscal Year Ended March 31, 2017 1st Quarter 2nd Quarter 3rd Quarter 4th Quarter Total Year (in $000's) Revenue $ 102,995 $ 102,955 $ 114,674 $ 124,680 $ 445,304 Cost of revenue 15,070 17,309 18,987 19,261 70,627 Other operating expenses 66,692 71,138 70,284 76,425 284,539 Other income, net 192 228 423 362 1,205 Income before income taxes 21,425 14,736 25,826 29,356 91,343 Income tax provision 8,515 5,861 10,394 14,457 39,227 Net income $ 12,910 $ 8,875 $ 15,432 $ 14,899 $ 52,116 Basic net income per share $ 0.30 $ 0.21 $ 0.36 $ 0.34 $ 1.21 Diluted net income per share $ 0.29 $ 0.20 $ 0.34 $ 0.33 $ 1.17

Summary of Significant Accoun34

Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Mar. 31, 2018USD ($)Customershares	Mar. 31, 2017USD ($)Customershares	Mar. 31, 2016USD ($)Customershares	Apr. 01, 2017USD ($)
Summary Of Significant Accounting Policy [Line Items]
Product warranty period	1 year
Reclassifications out of accumulated other comprehensive income (loss)	$ 0	$ 0	$ 0
Expected dividend yield	0.00%
Excess tax benefits related to restricted stock unit vestings or stock option exercises, decrease in financing activities		12,038,000	3,567,000
Excess tax benefits related to restricted stock unit vestings or stock option exercises, increase in operating activities		$ 12,038,000	$ 3,567,000
ASU 2016-09
Summary Of Significant Accounting Policy [Line Items]
Excess tax benefit	$ 31,000,000
Excess tax benefits related to restricted stock unit vestings or stock option exercises, decrease in financing activities	31,000,000
Excess tax benefits related to restricted stock unit vestings or stock option exercises, increase in operating activities	$ 31,000,000
Increase additional paid in capital				$ 1,800,000
Increase deferred tax assets				700,000
Decrease retained earnings				(1,100,000)
Adjustment to Increase Retained Earnings and Deferred Tax Assets | ASU 2016-09
Summary Of Significant Accounting Policy [Line Items]
Cumulative effect to increase retained earnings and deferred tax assets				$ 76,400,000
Stock Options and Performance Shares
Summary Of Significant Accounting Policy [Line Items]
Shares excluded from the calculation of diluted weighted average shares outstanding | shares	155,000	24,000	62,000
Leasehold Improvements
Summary Of Significant Accounting Policy [Line Items]
Leasehold improvements, useful life	shorter of the lease term or the estimated useful lives
Minimum | Machinery and Equipment
Summary Of Significant Accounting Policy [Line Items]
Property and Equipment, useful life	3 years
Minimum | Computer Software
Summary Of Significant Accounting Policy [Line Items]
Property and Equipment, useful life	3 years
Minimum | Furniture and Fixtures
Summary Of Significant Accounting Policy [Line Items]
Property and Equipment, useful life	3 years
Minimum | Building and Building Improvements
Summary Of Significant Accounting Policy [Line Items]
Property and Equipment, useful life	7 years
Maximum | Machinery and Equipment
Summary Of Significant Accounting Policy [Line Items]
Property and Equipment, useful life	5 years
Maximum | Computer Software
Summary Of Significant Accounting Policy [Line Items]
Property and Equipment, useful life	5 years
Maximum | Furniture and Fixtures
Summary Of Significant Accounting Policy [Line Items]
Property and Equipment, useful life	5 years
Maximum | Building and Building Improvements
Summary Of Significant Accounting Policy [Line Items]
Property and Equipment, useful life	33 years
Customer Concentration Risk | Total Revenues
Summary Of Significant Accounting Policy [Line Items]
Number of customer accounted more than 10% of total revenue / total receivable | Customer	0	0	0
Customer Concentration Risk | Total Revenues | Minimum
Summary Of Significant Accounting Policy [Line Items]
Percentage of concentration risk	10.00%	10.00%	10.00%
Customer Concentration Risk | Total Accounts Receivable
Summary Of Significant Accounting Policy [Line Items]
Number of customer accounted more than 10% of total revenue / total receivable | Customer	0	0
Customer Concentration Risk | Total Accounts Receivable | Minimum
Summary Of Significant Accounting Policy [Line Items]
Percentage of concentration risk	10.00%	10.00%

Computation of Basic and Dilute

Computation of Basic and Diluted Net Income Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Basic Net Income Per Share
Net income	$ 36,847	$ 13,446	$ 24,503	$ 37,374	$ 14,899	$ 15,432	$ 8,875	$ 12,910	$ 112,170	$ 52,116	$ 38,147
Weighted average shares used in computing basic net income per share									44,153	43,238	42,204
Net income per share - basic	$ 0.83	$ 0.30	$ 0.56	$ 0.85	$ 0.34	$ 0.36	$ 0.21	$ 0.30	$ 2.54	$ 1.21	$ 0.90
Diluted Net Income Per Share
Net income	$ 36,847	$ 13,446	$ 24,503	$ 37,374	$ 14,899	$ 15,432	$ 8,875	$ 12,910	$ 112,170	$ 52,116	$ 38,147
Weighted average shares used in computing basic net income per share									44,153	43,238	42,204
Effect of dilutive securities									1,696	1,420	2,691
Weighted average shares used in computing diluted net income per share									45,849	44,658	44,895
Net income per share - diluted	$ 0.80	$ 0.29	$ 0.54	$ 0.82	$ 0.33	$ 0.34	$ 0.20	$ 0.29	$ 2.45	$ 1.17	$ 0.85

Schedule of Changes in Beginnin

Schedule of Changes in Beginning Stockholders' Equity (Detail) - USD ($) $ in Thousands	Apr. 01, 2017	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
Balance	$ 529,152	$ 689,524	$ 452,071	$ 368,775	$ 291,560
Common stock, Outstanding		44,375,337	43,673,286
Cumulative effect of adoption of new accounting standard	77,081
Common Stock
Balance	$ 437	$ 444	$ 437	$ 426	$ 413
Common stock, Outstanding	43,673,286	44,375,337	43,673,286	42,596,228	41,335,773
Treasury Stock
Balance	$ (46,763)	$ (67,078)	$ (46,763)	$ (26,660)	$ (19,347)
Common stock, Outstanding	1,575,995	1,725,312	1,575,995	1,376,891	1,282,944
Additional Paid in Capital
Balance	$ 567,797	$ 619,905	$ 565,962	$ 508,624	$ 465,046
Cumulative effect of adoption of new accounting standard	1,835
Accumulated Deficit
Balance	28,287	140,457	(46,959)	(99,075)	(137,222)
Cumulative effect of adoption of new accounting standard	75,246
Accumulated Other Comprehensive Income (Loss)
Balance	$ (20,606)	$ (4,204)	$ (20,606)	$ (14,540)	$ (17,330)

Cash Equivalents and Marketable

Cash Equivalents and Marketable Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Mar. 31, 2017
Fair Value Disclosures [Abstract]
Cash equivalents (within 90 days at the time of purchase to maturity)	$ 22,595	$ 23,975
Short-term marketable securities (within one year to maturity)	319,274	190,908
Long-term marketable securities (one to two years to maturity)	37,502	47,143
Available-for-sale securities, fair value disclosure	$ 379,371	$ 262,026

Cash Equivalents and Marketab38

Cash Equivalents and Marketable Securities (Parenthetical) (Detail)	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Maximum
Investment [Line Items]
Cash equivalents, maturity period	90 days	90 days
Short-term marketable securities, maturity period	1 year	1 year
Long-term marketable securities, maturity period	2 years	2 years
Minimum
Investment [Line Items]
Long-term marketable securities, maturity period	1 year	1 year

Investable Cash Equivalents and

Investable Cash Equivalents and Marketable Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Mar. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	$ 380,183	$ 262,173
Gross Unrealized Gains	7	6
Gross Unrealized Losses	(819)	(153)
Fair Market Value	379,371	262,026
Repurchase Agreement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	16,750	12,000
Fair Market Value	16,750	12,000
Commercial Paper | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	36,936	42,304
Gross Unrealized Gains	2
Gross Unrealized Losses	(63)	(25)
Fair Market Value	36,875	42,279
Money Market Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	5,845	11,975
Fair Market Value	5,845	11,975
U.S. Treasury mutual fund securities | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	18,132	45,199
Gross Unrealized Losses	(29)	(13)
Fair Market Value	18,103	45,186
U.S. Treasury mutual fund securities | Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	10,953	1,998
Gross Unrealized Losses	(16)	(3)
Fair Market Value	10,937	1,995
Government-backed securities | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	212,255	90,199
Gross Unrealized Gains	3	1
Gross Unrealized Losses	(538)	(87)
Fair Market Value	211,720	90,113
Government-backed securities | Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	24,798	43,484
Gross Unrealized Gains	1	5
Gross Unrealized Losses	(12)	(18)
Fair Market Value	24,787	43,471
Corporate Debt Securities | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	52,737	13,161
Gross Unrealized Losses	(161)	(6)
Fair Market Value	52,576	13,155
Corporate Debt Securities | Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	1,777	1,853
Gross Unrealized Gains	1
Gross Unrealized Losses		(1)
Fair Market Value	$ 1,778	$ 1,852

Financial Instruments Measured

Financial Instruments Measured at Fair Value (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Mar. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	$ 379,371	$ 262,026
Contingent consideration	10,490	9,153
Repurchase Agreement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	16,750	12,000
Commercial Paper | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	36,875	42,279
Level 2 | Repurchase Agreement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	16,750	12,000
Level 2 | Commercial Paper | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	36,875	42,279
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration	10,490	9,153
Money Market Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	5,845	11,975
Money Market Funds | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	5,845	11,975
U.S. Treasury mutual fund securities | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	18,103	45,186
U.S. Treasury mutual fund securities | Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	10,937	1,995
U.S. Treasury mutual fund securities | Level 2 | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	18,103	45,186
U.S. Treasury mutual fund securities | Level 2 | Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	10,937	1,995
Government-backed securities | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	211,720	90,113
Government-backed securities | Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	24,787	43,471
Government-backed securities | Level 2 | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	211,720	90,113
Government-backed securities | Level 2 | Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	24,787	43,471
Corporate Debt Securities | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	52,576	13,155
Corporate Debt Securities | Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	1,778	1,852
Corporate Debt Securities | Level 2 | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	52,576	13,155
Corporate Debt Securities | Level 2 | Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	$ 1,778	$ 1,852

Cash Equivalents, Marketable 41

Cash Equivalents, Marketable Securities and Fair Value Measurements - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Jul. 31, 2014	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Aggregate carrying amount of portfolio of other investments		$ 12,600	$ 7,200
Investments in private medical device company		$ 6,400	$ 2,899	$ 750
ECP Entwicklungsgesellschaft mbH
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payments to acquire businesses, cash paid	$ 13,000
Potential payouts payments	$ 15,000

Valuation Method Used to Calcul

Valuation Method Used to Calculate Level 3 Liabilities Measured at Estimated Fair Value of Contingent Consideration Related to Acquisition (Detail) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Jul. 31, 2014	Mar. 31, 2018	Mar. 31, 2017
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Contingent consideration		$ 10,490	$ 9,153
ECP Entwicklungsgesellschaft mbH
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Discount rate	21.50%
Level 3
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Contingent consideration		10,490	$ 9,153
Level 3 | ECP Entwicklungsgesellschaft mbH
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Contingent consideration		10,490
Level 3 | ECP Entwicklungsgesellschaft mbH | Probability weighted income approach | Clinical and regulatory milestone
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Contingent consideration		$ 5,631
Level 3 | ECP Entwicklungsgesellschaft mbH | Probability weighted income approach | Clinical and regulatory milestone | Base Case Scenario | Contingent Consideration
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Probability of occurrence		40.00%
Level 3 | ECP Entwicklungsgesellschaft mbH | Probability weighted income approach | Clinical and regulatory milestone | Minimum | Contingent Consideration
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Projected fiscal year of milestone payments		2,019
Discount rate		3.20%
Level 3 | ECP Entwicklungsgesellschaft mbH | Probability weighted income approach | Clinical and regulatory milestone | Minimum | Various Upside and Downside Scenarios | Contingent Consideration
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Probability of occurrence		12.00%
Level 3 | ECP Entwicklungsgesellschaft mbH | Probability weighted income approach | Clinical and regulatory milestone | Maximum | Contingent Consideration
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Projected fiscal year of milestone payments		2,022
Discount rate		3.80%
Level 3 | ECP Entwicklungsgesellschaft mbH | Probability weighted income approach | Clinical and regulatory milestone | Maximum | Various Upside and Downside Scenarios | Contingent Consideration
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Probability of occurrence		30.00%
Level 3 | ECP Entwicklungsgesellschaft mbH | Monte Carlo simulation model | Revenue-based milestone
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Contingent consideration		$ 4,859
Level 3 | ECP Entwicklungsgesellschaft mbH | Monte Carlo simulation model | Revenue-based milestone | Contingent Consideration
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Discount rate		18.00%
Expected volatility for forecasted revenues		50.00%
Probability of payment (risk neutral)		78.50%
Level 3 | ECP Entwicklungsgesellschaft mbH | Monte Carlo simulation model | Revenue-based milestone | Minimum | Contingent Consideration
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Projected fiscal year of milestone payments		2,023
Level 3 | ECP Entwicklungsgesellschaft mbH | Monte Carlo simulation model | Revenue-based milestone | Maximum | Contingent Consideration
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Projected fiscal year of milestone payments		2,035

Change in Fair Value of Conting

Change in Fair Value of Contingent Consideration as Determined by Level 3 Inputs (Detail) - Contingent Consideration - ECP Entwicklungsgesellschaft mbH - Level 3 - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Level 3 liabilities, beginning balance	$ 9,153	$ 7,563	$ 6,510
Additions	0	0	0
Payments	0	0	0
Change in fair value	1,337	1,590	1,053
Level 3 liabilities, ending balance	$ 10,490	$ 9,153	$ 7,563

Components of Accounts Receivab

Components of Accounts Receivable (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
Receivables [Abstract]
Trade receivables	$ 70,330	$ 54,337
Allowance for doubtful accounts	(320)	(282)	$ (124)	$ (177)
Accounts receivable, net	$ 70,010	$ 54,055

Summary of Allowance for Doubtf

Summary of Allowance for Doubtful Accounts Receivable (Detail) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Receivables [Abstract]
Balance at Beginning of Period	$ 282	$ 124	$ 177
Additions	38	159	42
Write-offs		(1)	(95)
Balance at End of Period	$ 320	$ 282	$ 124

Components of Inventories (Deta

Components of Inventories (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Mar. 31, 2017
Inventory Disclosure [Abstract]
Raw materials and supplies	$ 16,481	$ 9,784
Work-in-progress	23,179	16,504
Finished goods	10,544	8,643
Inventories	$ 50,204	$ 34,931

Components of Property and Equi

Components of Property and Equipment (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Mar. 31, 2017
Property Plant And Equipment [Abstract]
Land	$ 7,680	$ 4,046
Building and building improvements	63,700	10,900
Capital lease asset		16,784
Leasehold improvements	2,905	34,854
Machinery and equipment	42,787	27,989
Furniture and fixtures	8,104	3,899
Construction in progress	19,850	9,257
Total cost	145,026	107,729
Less accumulated depreciation	(27,859)	(19,952)
Property and equipment, net	$ 117,167	$ 87,777

Property and Equipment - Additi

Property and Equipment - Additional Information (Detail) $ in Thousands	1 Months Ended		12 Months Ended
	Oct. 31, 2017USD ($)	Feb. 28, 2017USD ($)ft²	Mar. 31, 2018USD ($)	Mar. 31, 2017USD ($)	Mar. 31, 2016USD ($)
Property Plant And Equipment [Line Items]
Acquisition cost for property and equipment			$ 55,863	$ 50,415	$ 15,624
Depreciation expense			$ 11,000	$ 6,200	$ 3,300
Danvers
Property Plant And Equipment [Line Items]
Reclassification of leasehold improvement to building and building improvements	$ 32,600
Danvers | Land and Building
Property Plant And Equipment [Line Items]
Acquisition cost for property and equipment	16,500
Danvers | Land
Property Plant And Equipment [Line Items]
Acquisition cost for property and equipment	3,000
Danvers | Building and Building Improvements
Property Plant And Equipment [Line Items]
Acquisition cost for property and equipment	$ 13,000
Europe | Lease Agreements
Property Plant And Equipment [Line Items]
Office space under lease | ft²		33,000
Europe | Land and Building
Property Plant And Equipment [Line Items]
Acquisition cost for property and equipment		$ 12,600
Europe | Land
Property Plant And Equipment [Line Items]
Acquisition cost for property and equipment		4,000
Europe | Building and Building Improvements
Property Plant And Equipment [Line Items]
Acquisition cost for property and equipment		$ 8,600

Goodwill and In-Process Resea49

Goodwill and In-Process Research and Development - Additional Information (Detail) - USD ($)	1 Months Ended
	Jul. 31, 2014	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Goodwill [Line Items]
Goodwill		$ 35,808,000	$ 31,045,000	$ 33,003,000
Accumulated impairment loss, goodwill		0
In-process research and development		$ 16,705,000	$ 14,482,000	$ 15,396,000
ECP Entwicklungsgesellschaft mbH
Goodwill [Line Items]
In-process research and development	$ 18,500,000
Fair value inputs, discount rate	21.50%

Goodwill Activity (Detail)

Goodwill Activity (Detail) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Goodwill And Intangible Assets Disclosure [Abstract]
Beginning balance	$ 31,045	$ 33,003
Foreign currency translation impact	4,763	(1,958)
Ending balance	$ 35,808	$ 31,045

Carrying value of In-Process Re

Carrying value of In-Process Research and Development (Detail) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Goodwill And Intangible Assets Disclosure [Abstract]
Beginning balance	$ 14,482	$ 15,396
Foreign currency translation impact	2,223	(914)
Ending balance	$ 16,705	$ 14,482

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail) - $ / shares	Mar. 31, 2018	Mar. 31, 2017
Stockholders Equity Note [Abstract]
Class B Preferred Stock, par value	$ 0.01	$ 0.01
Class B Preferred Stock, Authorized	1,000,000	1,000,000
Class B Preferred Stock, Issued	0	0
Class B Preferred Stock, outstanding	0	0

Stock Award Plans and Stock-B53

Stock Award Plans and Stock-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended					12 Months Ended
	May 31, 2017	Nov. 30, 2016	May 31, 2016	Jun. 30, 2015	May 31, 2015	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate intrinsic value of options exercised in period						$ 66,400	$ 74,800	$ 58,600
Proceeds from the exercise of stock options						$ 9,303	$ 10,660	$ 9,771
Expected dividend yield						0.00%
2015 Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option conversion description						Each share of stock issued pursuant to a stock option or stock appreciation right counts as one share against the maximum number of shares issuable under the 2015 Plan, while each share of stock issued pursuant to any other type of award counts as 1.8 shares against the maximum number of shares issuable under the 2015 Plan.
Shares available for future issuance under the Plan						2,542,000
2008 Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future issuance under the Plan						270,000
Description of share counts for awards other than 2008 Stock Incentive Plan						Each share of stock currently issued pursuant to any other type of award counts as 1.58 shares against the maximum number of shares issuable under the 2008 Plan
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock award plans, outstanding stock options expiration period						10 years
Vesting period						3 years
Unrecognized stock-based compensation expense						$ 9,500
Unrecognized stock-based compensation expense, weighted-average recognition period						2 years 2 months 12 days
Expected dividend yield						0.00%
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period						3 years
Unrecognized stock-based compensation expense						$ 32,200
Unrecognized stock-based compensation expense, weighted-average recognition period						1 year 9 months 18 days
Expected dividend yield		0.00%		0.00%
Weighted average grant-date fair value for restricted stock and restricted stock units granted						$ 137.40	$ 97.43	$ 87.45
Fair value of restricted stock and restricted stock units vested in period						$ 51,000	$ 51,300	$ 39,600
Restricted share unit issued						296,000
Non-vested shares, outstanding						880,000	1,056,000
Share based payment award vesting term						2018-06
Share based compensation arrangement performance period						3 years
Equity award, vesting options						One-half of the restricted stock units will potentially vest in June 2018 based on performance criteria described above and the remaining half of the restricted stock units will vest one year thereafter.
Restricted Stock Units | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted Share earning						0.00%
Restricted Stock Units | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted Share earning						100.00%
Restricted Stock Units | Executive Office
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted share unit issued		41,526
Performance and Market-Based Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized stock-based compensation expense						$ 14,500
Unrecognized stock-based compensation expense, weighted-average recognition period						1 year 9 months 18 days
Performance Based Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted share unit issued	159,000		190,890		183,940
Performance Based Restricted Stock Units Issued in May 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-vested shares, outstanding						152,000
Performance Based Restricted Stock Units Issued in May 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-vested shares, outstanding						82,000
Performance Based Restricted Stock Units Issued in May 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-vested shares, outstanding						55,000
Market Based Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based payment award vesting term						2018-06
Share based compensation arrangement performance period						3 years
Equity award, vesting options						One-half of the market-based restricted stock units earned will vest in June 2018 and the remaining restricted stock units will vest one year thereafter provided the executive officers are still employed with the Company.
Market Based Restricted Stock Units | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted Share earning						0.00%
Market Based Restricted Stock Units | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted Share earning						300.00%
Market Based Restricted Stock Units | Chief Financial Officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted share unit issued				322,980
Non-vested shares, outstanding				281,530
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
ESPP, exercise price as a percentage of its market price						85.00%

Stock-Based Compensation Recogn

Stock-Based Compensation Recognized (Detail) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation	$ 40,353	$ 32,866	$ 29,053
Cost of revenue
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation	1,721	1,061	895
Research and development
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation	5,895	6,050	3,950
Selling, general and administrative
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation	$ 32,737	$ 25,755	$ 24,208

Components of Stock-Based Compe

Components of Stock-Based Compensation (Detail) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation	$ 40,353	$ 32,866	$ 29,053
Restricted Stock Units
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation	34,559	26,570	23,708
Stock Options
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation	5,202	5,829	4,866
Employee Stock Purchase Plan
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation	$ 592	$ 467	$ 479

Summary of Stock Option Activit

Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Options
Outstanding at beginning of period	1,646
Granted	155
Exercised	(460)
Cancelled and expired	(59)
Outstanding at end of period	1,282	1,646
Exercisable at end of period	965
Options vested and expected to vest at end of period	1,259
Weighted Average Exercise Price
Outstanding at beginning of period	$ 32.09
Granted	143.52
Exercised	20.23
Cancelled and expired	98.21
Outstanding at end of period	46.81	$ 32.09
Exercisable at end of period	24.88
Options vested and expected to vest at end of period	$ 46.18
Weighted Average Remaining Contractual Term (years)
Outstanding	5 years 3 months 21 days	5 years 5 months 15 days
Exercisable at end of period	4 years 3 months 14 days
Options vested and expected to vest at end of period	5 years 3 months 7 days
Aggregate Intrinsic Value
Outstanding at end of period	$ 313,158
Exercisable at end of period	256,891
Options vested and expected to vest at end of period	$ 308,252

Summary of Weighted Average Gra

Summary of Weighted Average Grant-Date Fair Values And Weighted Average Assumptions Used to Calculate Fair Value of Options Granted (Detail) - Stock Options - $ / shares	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Valuation assumptions:
Weighted average grant-date fair value	$ 52.34	$ 42.40	$ 29.57
Risk-free interest rate	1.87%	1.41%	1.55%
Expected option life (years)	4 years 25 days	4 years 1 month 20 days	4 years 1 month 24 days
Expected volatility	43.50%	48.90%	49.70%

Summary of Restricted Stock Uni

Summary of Restricted Stock Units Activity (Detail) - Restricted Stock Units - $ / shares shares in Thousands	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Number of Shares
Beginning Balance	1,056
Granted	296
Vested	(372)
Forfeited	(100)
Ending Balance	880	1,056
Weighted Average Grant Date Fair Value
Beginning Balance	$ 80.50
Granted	137.40	$ 97.43	$ 87.45
Vested	53.40
Forfeited	98.47
Ending Balance	$ 109.01	$ 80.50

Monte Carlo Simulation Model to

Monte Carlo Simulation Model to Estimate Grant-Date Fair Value of Restricted Stock Units (Detail) - $ / shares	1 Months Ended		12 Months Ended
	Nov. 30, 2016	Jun. 30, 2015	Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend yield			0.00%
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	0.90%	1.10%
Dividend yield	0.00%	0.00%
Remaining performance period (years)	2 months 15 days	2 months 15 days
Expected volatility	50.60%	47.20%
Estimated grant date fair value (per share)	$ 62.55
Target performance (number of shares)	41,526	107,660
Restricted Stock Units | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Estimated grant date fair value (per share)		$ 93.49
Restricted Stock Units | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Estimated grant date fair value (per share)		$ 107.10

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	Jan. 01, 2018	Dec. 31, 2017	Mar. 31, 2018		Dec. 31, 2017	[1],[2]	Sep. 30, 2017	[1],[2]	Jun. 30, 2017	[1],[2]	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2018		Mar. 31, 2017	Mar. 31, 2016
Income Taxes [Line Items]
U.S. federal statutory corporate tax rate	21.00%	35.00%													31.50%		35.00%	35.00%
Blended U.S. federal statutory corporate income tax rate															31.50%
Income tax provision			$ 11,660,000	[1],[2]	$ 32,208,000		$ 7,981,000		$ (3,582,000)		$ 14,457,000	$ 10,394,000	$ 5,861,000	$ 8,515,000	$ 48,267,000	[1],[2]	$ 39,227,000	$ 27,691,000
Effective income tax rate															30.10%		43.00%	42.10%
Measurement period															1 year
Income tax expense															$ 21,400,000
Valuation allowance			1,652,000								$ 2,468,000				1,652,000		$ 2,468,000
Net operating loss carry forwards			72,200,000												72,200,000
Interest and penalties															$ 0		$ 0	$ 0
Earliest Tax Year
Income Taxes [Line Items]
Net operating loss carry forwards expiration period															2,019
Latest Tax Year
Income Taxes [Line Items]
Net operating loss carry forwards expiration period															2,035
Foreign
Income Taxes [Line Items]
Net operating loss carry forwards			3,900,000												$ 3,900,000
Federal
Income Taxes [Line Items]
Research and development credit carry forwards			16,600,000												16,600,000
State
Income Taxes [Line Items]
Research and development credit carry forwards			$ 9,000,000												9,000,000
ASU 2016-09
Income Taxes [Line Items]
Excess tax benefits from stock-based awards															$ 31,000,000
[1]	In the first quarter of fiscal 2018, the Company adopted Accounting Standards Update No. 2016-09, Improvements to Employee Share-Based Payment Accounting, which requires that all excess tax benefits and tax deficiencies related share-based compensation arrangements be recognized as income tax benefit or expense, instead of in stockholders’ equity as previous guidance required. The income tax benefit for the year ended March 31, 2018 included excess tax benefits of $31.0 million. These recognized excess tax benefits resulted from restricted stock units that vested or stock options that were exercised during the year ended March 31, 2018.
[2]	On December 22, 2017, the Tax Cuts and Jobs Act, or Tax Reform Act, was enacted into law. This new law, among other items, reduces the U.S. federal statutory corporate income tax rate from 35% to 21% effective January 1, 2018. During the year ended March 31, 2018, the Company recorded tax expense adjustments for $21.4 million related to the revaluation of its deferred taxes due to a reduction of the U.S. federal statutory corporate income tax rate.

Components of Income Tax Provis

Components of Income Tax Provision (Detail) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Mar. 31, 2018	[1],[2]	Dec. 31, 2017	[1],[2]	Sep. 30, 2017	[1],[2]	Jun. 30, 2017	[1],[2]	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2018		Mar. 31, 2017	Mar. 31, 2016
Income Tax Disclosure [Abstract]
Income (loss) before income taxes													$ 134,006		$ 78,172	$ 54,406
Income (loss) before income taxes, foreign													26,431		13,170	11,432
Income (loss) before income taxes													160,437		91,342	65,838
Current income tax provision, Federal													752		7,313	1,690
Current income tax provision, State													1,491		5,045	2,113
Current income tax provision, Foreign													3,400		1,066	1,592
Current income tax provision													5,643		13,424	5,395
Deferred income tax provision, Federal													38,848		23,008	18,769
Deferred income tax provision, State													(1,014)		(349)	1,284
Deferred income tax provision, Foreign													4,790		3,144	2,243
Deferred income tax provision													42,624		25,803	22,296
Total income tax provision	$ 11,660		$ 32,208		$ 7,981		$ (3,582)		$ 14,457	$ 10,394	$ 5,861	$ 8,515	$ 48,267	[1],[2]	$ 39,227	$ 27,691
[1]	In the first quarter of fiscal 2018, the Company adopted Accounting Standards Update No. 2016-09, Improvements to Employee Share-Based Payment Accounting, which requires that all excess tax benefits and tax deficiencies related share-based compensation arrangements be recognized as income tax benefit or expense, instead of in stockholders’ equity as previous guidance required. The income tax benefit for the year ended March 31, 2018 included excess tax benefits of $31.0 million. These recognized excess tax benefits resulted from restricted stock units that vested or stock options that were exercised during the year ended March 31, 2018.
[2]	On December 22, 2017, the Tax Cuts and Jobs Act, or Tax Reform Act, was enacted into law. This new law, among other items, reduces the U.S. federal statutory corporate income tax rate from 35% to 21% effective January 1, 2018. During the year ended March 31, 2018, the Company recorded tax expense adjustments for $21.4 million related to the revaluation of its deferred taxes due to a reduction of the U.S. federal statutory corporate income tax rate.

Components of Net Deferred Taxe

Components of Net Deferred Taxes (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Mar. 31, 2017
Deferred tax assets
Non-operating loss and tax credit carryforwards	$ 48,724	$ 8,814
Stock-based compensation	13,271	16,560
Nondeductible reserves and accruals	8,290	10,303
Foreign non-operating loss carryforwards	9,598	13,634
Deferred revenue	3,770	4,308
Depreciation and amortization	826	2,135
Other, net	822	1,308
Deferred Tax Assets, Gross, Total	85,301	57,062
Deferred tax liabilities
Goodwill	(6,787)	(9,444)
In-process research and development	(5,045)	(4,374)
Depreciation	(1,011)
Domestic deferred tax liability on foreign non-operating loss carryforwards	(963)	(6,836)
Deferred Tax Liabilities, Net	(13,806)	(20,654)
Net deferred tax assets	71,495	36,408
Valuation allowance	(1,652)	(2,468)
Net deferred tax assets	69,843	33,940
Long-term deferred tax assets, net	70,746	34,723
Long-term deferred tax liabilities	(903)	(783)
Net deferred tax assets	$ 69,843	$ 33,940

Differences Between Federal Sta

Differences Between Federal Statutory Income Tax Rate and Effective Tax Rates (Detail)	Jan. 01, 2018	Dec. 31, 2017	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Income Tax Disclosure [Abstract]
Statutory income tax rate	21.00%	35.00%	31.50%	35.00%	35.00%
Change in valuation allowance			0.50%	0.20%	0.70%
Credits			(4.90%)	(3.30%)	(4.10%)
Foreign taxes			2.20%	2.00%	2.50%
State taxes, net			2.00%	3.80%	3.70%
Permanent differences			2.40%	3.30%	3.00%
Stock-based compensation			(17.20%)	0.20%	0.30%
Rate differential on foreign operations				0.10%
Effect of the Tax Reform Act on net deferred tax assets			13.00%
Other			0.60%	1.70%	1.00%
Effective tax rate			30.10%	43.00%	42.10%

Changes in Valuation Allowance

Changes in Valuation Allowance for Deferred Tax Assets (Detail) - Valuation Allowance of Deferred Tax Assets - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Valuation Allowance [Line Items]
Balance at beginning of year	$ 2,468	$ 2,418	$ 2,912
Increases	325	50	677
Decreases	(1,141)		(1,171)
Balance at end of year	$ 1,652	$ 2,468	$ 2,418

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail)	Mar. 06, 2018USD ($)	Mar. 31, 2018ft²	Dec. 31, 2017USD ($)ft²	Oct. 31, 2017USD ($)	Feb. 28, 2017ft²	Oct. 31, 2016USD ($)	Sep. 30, 2016USD ($)	May 31, 2016	Sep. 30, 2015Patent	Mar. 31, 2018USD ($)ft²	Apr. 30, 2014USD ($)
Commitments and Contingencies [Line Items]
Potential payments agreed under license agreements											$ 6,000,000
License agreement, milestones payments										$ 3,500,000
License agreement, upfront payment										$ 1,500,000
Magnetic Clutch Patents
Commitments and Contingencies [Line Items]
Patents allegedly infringed upon, number | Patent									2
European Pigtail Patent
Commitments and Contingencies [Line Items]
Patents allegedly infringed upon, number | Patent									1
German Pigtail Patent
Commitments and Contingencies [Line Items]
Patents allegedly infringed upon, number | Patent									1
Patent One
Commitments and Contingencies [Line Items]
Patent expiration period								2020-09
Patent Two
Commitments and Contingencies [Line Items]
Patent expiration period								2020-12
Patent Three
Commitments and Contingencies [Line Items]
Patent expiration period								2021-10
Settlement Agreement
Commitments and Contingencies [Line Items]
Litigation settlement agreement date	March 6, 2018
Settlement Agreement | Former Employee
Commitments and Contingencies [Line Items]
Litigation settlement, agreed to pay amount	$ 150,000
Settlement Agreement | U.S. Government
Commitments and Contingencies [Line Items]
Litigation settlement, agreed to pay amount	3,100,000
Litigation settlement, agreed to pay accrued interest	$ 30,000
Lease Agreements
Commitments and Contingencies [Line Items]
Corporate headquarters acquisition				$ 16,500,000
Lease Agreements | Massachusetts
Commitments and Contingencies [Line Items]
Additional office space | ft²		11,269	6,607		21,603					11,269
Lease expiration date					Jul. 31, 2022
Extend lease term		Aug. 31, 2025	Aug. 31, 2025
Annual rent expense			$ 400,000
Lease Agreements | Germany
Commitments and Contingencies [Line Items]
Annual rent expense							$ 300,000
Lease commencement period							2017-05
Lease expiration period							2024-05
Lease Agreements | Japan
Commitments and Contingencies [Line Items]
Annual rent expense						$ 900,000
Lease expiration period						2021-09

Future Minimum Lease Payments U

Future Minimum Lease Payments Under Non-Cancelable Leases (Detail) $ in Thousands	Mar. 31, 2018USD ($)
Leases [Abstract]
2,019	$ 2,078
2,020	1,888
2,021	1,901
2,022	1,408
2,023	891
Thereafter	1,923
Total minimum lease payments	$ 10,089

Accrued Expenses (Detail)

Accrued Expenses (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Mar. 31, 2017
Payables and Accruals [Abstract]
Employee compensation	$ 30,330	$ 23,290
Sales and income taxes	4,562	3,180
Research and development	3,162	2,349
Marketing	2,305	1,827
Professional, legal and accounting fees	1,870	2,019
Warranty	1,081	717
Accrued capital expenditures	250	2,300
Other	2,587	2,021
Accrued expenses	$ 46,147	$ 37,703

Segment and Enterprise Wide D68

Segment and Enterprise Wide Disclosures - Additional Information (Detail) $ in Millions	12 Months Ended
	Mar. 31, 2018USD ($)Segment	Mar. 31, 2017USD ($)	Mar. 31, 2016
Segment Reporting Information [Line Items]
Number of business segments | Segment	1
International
Segment Reporting Information [Line Items]
Long-lived assets | $	$ 35.5	$ 23.2
Customer Concentration Risk | Total Revenues | International
Segment Reporting Information [Line Items]
Percentage of revenue accounted	11.00%	9.00%	8.00%

Summary of Unaudited Quarterly

Summary of Unaudited Quarterly Results of Operations (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended												12 Months Ended
	Mar. 31, 2018		Dec. 31, 2017		Sep. 30, 2017		Jun. 30, 2017		Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2018		Mar. 31, 2017	Mar. 31, 2016
Disclosure Unaudited Quarterly Financial Information [Abstract]
Revenue	$ 174,436		$ 154,022		$ 132,823		$ 132,468		$ 124,680	$ 114,674	$ 102,955	$ 102,995	$ 593,749		$ 445,304	$ 329,543
Cost of revenue	30,098		24,994		21,627		21,862		19,261	18,987	17,309	15,070	98,581		70,627	50,419
Other operating expenses	96,771		84,262		79,470		77,528		76,425	70,284	71,138	66,692	338,031		284,539
Other income, net	940		888		758		714		362	423	228	192	3,300		1,205	734
Income before income taxes	48,507		45,654		32,484		33,792		29,356	25,826	14,736	21,425	160,437		91,343	65,838
Income tax (benefit) provision	11,660	[1],[2]	32,208	[1],[2]	7,981	[1],[2]	(3,582)	[1],[2]	14,457	10,394	5,861	8,515	48,267	[1],[2]	39,227	27,691
Net income	$ 36,847		$ 13,446		$ 24,503		$ 37,374		$ 14,899	$ 15,432	$ 8,875	$ 12,910	$ 112,170		$ 52,116	$ 38,147
Basic net income per share	$ 0.83		$ 0.30		$ 0.56		$ 0.85		$ 0.34	$ 0.36	$ 0.21	$ 0.30	$ 2.54		$ 1.21	$ 0.90
Diluted net income per share	$ 0.80		$ 0.29		$ 0.54		$ 0.82		$ 0.33	$ 0.34	$ 0.20	$ 0.29	$ 2.45		$ 1.17	$ 0.85
[1]	In the first quarter of fiscal 2018, the Company adopted Accounting Standards Update No. 2016-09, Improvements to Employee Share-Based Payment Accounting, which requires that all excess tax benefits and tax deficiencies related share-based compensation arrangements be recognized as income tax benefit or expense, instead of in stockholders’ equity as previous guidance required. The income tax benefit for the year ended March 31, 2018 included excess tax benefits of $31.0 million. These recognized excess tax benefits resulted from restricted stock units that vested or stock options that were exercised during the year ended March 31, 2018.
[2]	On December 22, 2017, the Tax Cuts and Jobs Act, or Tax Reform Act, was enacted into law. This new law, among other items, reduces the U.S. federal statutory corporate income tax rate from 35% to 21% effective January 1, 2018. During the year ended March 31, 2018, the Company recorded tax expense adjustments for $21.4 million related to the revaluation of its deferred taxes due to a reduction of the U.S. federal statutory corporate income tax rate.

Summary of Unaudited Quarterl70

Summary of Unaudited Quarterly Results of Operations (Parenthetical) (Detail) - USD ($) $ in Millions	Jan. 01, 2018	Dec. 31, 2017	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Schedule Of Quarterly Financial Data [Line Items]
U.S. federal statutory corporate tax rate	21.00%	35.00%	31.50%	35.00%	35.00%
Income tax expense			$ 21.4
ASU 2016-09
Schedule Of Quarterly Financial Data [Line Items]
Excess tax benefit			$ 31