Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Operating activities:
Net income	$ 259,016	$ 112,170	$ 52,116
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	14,121	11,005	6,202
Bad debt expense	720	38	159
Stock-based compensation	54,494	40,353	32,866
Write-down of inventory and other	4,252	3,946	3,085
Accretion on marketable securities	(2,744)
Change in fair value of other investments	(30,161)
Excess tax benefit from stock-based awards			(12,038)
Deferred tax provision	(7,745)	42,624	25,803
Change in fair value of contingent consideration	(915)	1,337	1,590
Changes in assets and liabilities:
Accounts receivable	(22,023)	(15,289)	(11,550)
Inventories	(37,181)	(15,686)	(12,284)
Prepaid expenses and other assets	(2,527)	(4,466)	(2,366)
Accounts payable	7,976	4,412	7,565
Accrued expenses and other liabilities	13,406	7,722	22,223
Deferred revenue	1,508	4,380	1,745
Net cash provided by operating activities	252,197	192,546	115,116
Investing activities:
Purchases of marketable securities	(361,602)	(325,408)	(278,501)
Proceeds from the sale and maturity of marketable securities and other	331,886	206,909	205,482
Purchases of other investments and intangible assets	(42,735)	(6,400)	(2,899)
Purchases of property and equipment	(44,004)	(55,863)	(50,415)
Net cash used for investing activities	(116,455)	(180,762)	(126,333)
Financing activities:
Proceeds from the exercise of stock options	12,949	9,303	10,660
Excess tax benefit from stock-based awards			12,038
Taxes paid related to net share settlement upon vesting of stock awards	(71,776)	(20,317)	(20,105)
Proceeds from the issuance of stock under employee stock purchase plan	3,052	2,394	1,720
Principal payments on capital lease obligation		(517)	(446)
Net cash (used for) provided by financing activities	(55,775)	(9,137)	3,867
Effect of exchange rate changes on cash	(1,921)	1,288	(1,841)
Net increase in cash and cash equivalents	78,046	3,935	(9,191)
Cash and cash equivalents at beginning of year	42,975	39,040	48,231
Cash and cash equivalents at end of year	121,021	42,975	39,040
Supplemental disclosure of cash flow information:
Cash paid for income taxes	5,290	4,641	1,405
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	$ 4,787	$ 3,338	$ 5,692