Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
Operating activities:
Net income	$ 52,116	$ 38,147	$ 113,688
Adjustments required to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	6,202	3,277	2,770
Bad debt expense	159	42	(5)
Stock-based compensation	32,866	29,053	16,520
Write-down of inventory	3,085	2,094	2,231
Excess tax benefit from stock-based awards	(12,038)	(3,567)	(606)
Deferred tax provision (benefit)	25,803	22,296	(87,094)
Change in fair value of contingent consideration	1,590	1,053	510
Changes in assets and liabilities:
Accounts receivable	(11,550)	(10,930)	(7,970)
Inventories	(12,284)	(11,473)	(6,967)
Prepaid expenses and other assets	(2,366)	(2,290)	(1,479)
Accounts payable	7,565	(2,645)	3,372
Accrued expenses and other liabilities	22,223	10,020	6,011
Deferred revenue	1,745	1,718	2,309
Net cash provided by operating activities	115,116	76,795	43,290
Investing activities:
Purchases of marketable securities	(278,501)	(260,975)	(97,658)
Proceeds from the sale and maturity of marketable securities	205,482	219,639	71,530
Acquisition of ECP and AIS, net of cash assumed			(15,697)
Purchase of other investment	(2,899)	(750)	(2,850)
Purchases of property and equipment	(50,415)	(15,624)	(5,188)
Net cash used for investing activities	(126,333)	(57,710)	(49,863)
Financing activities:
Proceeds from the exercise of stock options	10,660	9,771	10,927
Excess tax benefit from stock-based awards	12,038	3,567	606
Taxes paid related to net share settlement upon vesting of stock awards	(20,105)	(7,313)	(2,805)
Proceeds from the issuance of stock under employee stock purchase plan	1,720	1,135	795
Principal payments on capital lease obligation	(446)
Net cash provided by financing activities	3,867	7,160	9,523
Effect of exchange rate changes on cash	(1,841)	(415)	(1,465)
Net increase in cash and cash equivalents	(9,191)	25,830	1,485
Cash and cash equivalents at beginning of year	48,231	22,401	20,916
Cash and cash equivalents at end of year	39,040	48,231	22,401
Supplemental disclosure of cash flow information:
Cash paid for income taxes	1,405	848	1,215
Cash paid for interest on capital lease obligation	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	$ 5,692	$ 1,797	$ 193