CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 82,599	$ 68,392	$ 112,301
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	20,977	20,142	18,711
Amortization of debt issuance costs	1,450	1,208	0
Stock-based compensation	33,539	33,265	28,594
Excess tax benefit from stock-based compensation	(1,416)	(3,540)	(3,520)
Deferred income taxes	(657)	(8,291)	(980)
Provision for excess and obsolete inventories	1,960	2,430	931
Restructuring charges	(109)	16,160	0
Cash payments for restructuring charges	(4,001)	(10,385)	0
Other operating activities	2,948	7,680	(1,188)
Changes in assets and liabilities:
Accounts receivable	(13,894)	8,445	4,272
Inventory	(3,791)	1,357	128
Current and other assets	1,386	(605)	(5,368)
Accounts payable	4,377	5,407	(62)
Accrued liabilities	13,260	4,998	500
Income taxes	(657)	206	119
Cash provided by operating activities	137,971	146,869	154,438
CASH FLOWS FROM INVESTING ACTIVITIES
Proceeds from sales of investments	157,066	102,517	96,129
Proceeds from maturities of investments	144,092	97,164	120,430
Purchase of investments	(300,434)	(300,620)	(216,013)
Acquisition, net of cash acquired	0	0	(150)
Capital expenditures	(23,176)	(30,661)	(21,962)
Cash used for investing activities	(22,452)	(131,600)	(21,566)
CASH FLOWS FROM FINANCING ACTIVITIES
Repurchase of common stock	(34,236)	(497,393)	(112,939)
Employees' tax withheld and paid for restricted stock and restricted stock units	(9,736)	(11,068)	(7,611)
Proceeds from issuances under stock-based compensation plans	15,202	15,384	23,042
Payment of cash dividends	(19,959)	(21,061)	(25,730)
Proceeds from revolving line of credit	0	155,749	34,500
Repayments of revolving line of credit	0	(190,249)	0
Proceeds from bonds issuance, net of issuance costs	0	488,401	0
Excess tax benefit from stock-based compensation	1,416	3,540	3,520
Other financing activity	761	0	0
Cash used for financing activities	(46,552)	(56,697)	(85,218)
Effect of exchange rate changes on cash and cash equivalents	(2,263)	(156)	(3,508)
Net increase (decrease) in cash and cash equivalents	66,704	(41,584)	44,146
Cash and cash equivalents at beginning of year	235,266	276,850	232,704
Cash and cash equivalents at end of year	301,970	235,266	276,850
SUPPLEMENTAL DISCLOSURES
Cash paid for income taxes	20,948	25,517	33,804
Cash paid for interest	$ 27,783	$ 12,833	$ 0