CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ (869)	$ 82,599	$ 68,392
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	21,178	20,977	20,142
Amortization of debt issuance costs	1,450	1,450	1,208
Stock-based compensation	33,959	33,539	33,265
Deferred income taxes	7,464	(657)	(8,291)
Provision for excess and obsolete inventories	3,456	1,960	2,430
Restructuring charges	2,451	(109)	16,160
Cash payments for restructuring charges	(2,942)	(4,001)	(10,385)
Other operating activities	(305)	2,948	7,680
Changes in assets and liabilities:
Accounts receivable	(12,238)	(13,894)	8,445
Inventory	(13,309)	(3,791)	1,357
Current and other assets	(2,480)	1,386	(605)
Accounts payable	2,884	4,377	5,407
Accrued liabilities	(4,164)	13,260	4,998
Income taxes	84,613	(657)	206
Cash provided by operating activities	121,148	139,387	150,409
CASH FLOWS FROM INVESTING ACTIVITIES
Proceeds from sales of investments	197,575	157,066	102,517
Proceeds from maturities of investments	211,663	144,092	97,164
Purchase of investments	(373,281)	(300,434)	(300,620)
Capital expenditures	(12,468)	(23,176)	(30,661)
Cash used for investing activities	23,489	(22,452)	(131,600)
CASH FLOWS FROM FINANCING ACTIVITIES
Repurchase of common stock	(52,948)	(34,236)	(497,393)
Employees' tax withheld and paid for restricted stock and restricted stock units	(11,429)	(9,736)	(11,068)
Proceeds from issuances under stock-based compensation plans	23,927	15,202	15,384
Payment of cash dividends	(19,996)	(19,959)	(21,061)
Proceeds from revolving line of credit	8,000	0	155,749
Repayments of revolving line of credit	(8,000)	0	(190,249)
Proceeds from bonds issuance, net of issuance costs	0	0	488,401
Other financing activity	0	761	0
Cash used for financing activities	(60,446)	(47,968)	(60,237)
Effect of exchange rate changes on cash and cash equivalents	4,500	(2,263)	(156)
Net increase (decrease) in cash and cash equivalents	88,691	66,704	(41,584)
Cash and cash equivalents at beginning of year	301,970	235,266	276,850
Cash and cash equivalents at end of year	390,661	301,970	235,266
SUPPLEMENTAL DISCLOSURES
Cash paid for income taxes	9,757	20,948	25,517
Cash paid for interest	$ 27,899	$ 27,783	$ 12,833