Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Operating activities:
Net income	$ 203,009	$ 259,016	$ 112,170
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	20,430	14,121	11,005
Bad debt expense	487	720	38
Stock-based compensation	39,781	54,494	40,353
Write-down of inventory and other	4,249	4,252	3,946
Accretion on marketable securities	(2,731)	(2,744)
Change in fair value of other investments	5,184	(30,161)
Deferred tax provision	32,953	(7,745)	42,624
Change in fair value of contingent consideration	(575)	(915)	1,337
Other non-cash operating activities	4,108
Changes in assets and liabilities:
Accounts receivable	5,551	(22,023)	(15,289)
Inventories	(13,237)	(37,181)	(15,686)
Prepaid expenses and other assets	(5,333)	(2,527)	(4,466)
Accounts payable	2,581	7,976	4,412
Accrued expenses and other liabilities	15,676	13,406	7,722
Deferred revenue	2,787	1,508	4,380
Net cash provided by operating activities	314,920	252,197	192,546
Investing activities:
Purchases of marketable securities	(611,280)	(361,602)	(325,408)
Proceeds from the sale and maturity of marketable securities and other	550,788	331,886	206,909
Purchases of other investments and intangible assets	(20,957)	(42,735)	(6,400)
Purchases of property and equipment	(44,006)	(44,004)	(55,863)
Net cash used for investing activities	(125,455)	(116,455)	(180,762)
Financing activities:
Proceeds from the exercise of stock options	3,748	12,949	9,303
Taxes paid related to net share settlement upon vesting of stock awards	(41,687)	(71,776)	(20,317)
Repurchase of common stock	(84,879)
Proceeds from the issuance of stock under employee stock purchase plan	5,103	3,052	2,394
Principal payments on capital lease obligation			(517)
Net cash used for financing activities	(117,715)	(55,775)	(9,137)
Effect of exchange rate changes on cash	(430)	(1,921)	1,288
Net increase in cash and cash equivalents	71,320	78,046	3,935
Cash and cash equivalents at beginning of year	121,021	42,975	39,040
Cash and cash equivalents at end of year	192,341	121,021	42,975
Supplemental disclosure of cash flow information:
Cash paid for income taxes	9,685	5,290	4,641
Cash paid for interest on capital lease obligation			302
Supplemental disclosure of non-cash investing and financing activities:
Property and equipment in accounts payable and accrued expenses	2,977	$ 4,787	$ 3,338
Right-of-use assets obtained in exchange for lease liabilities	$ 15,650