CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2014
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 68,392	$ 112,301	$ 112,417
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	20,142	18,711	15,566
Amortization of debt issuance costs	1,208	0	0
Stock-based compensation	33,265	28,594	23,180
Excess tax benefit from stock-based compensation	(3,540)	(3,520)	(4,659)
Deferred income taxes	(8,291)	(980)	(5,813)
Provision for excess and obsolete inventories	2,430	931	4,138
Restructuring charges	16,160	0	547
Cash payments for restructuring charges	(10,385)	0	0
Other operating activities	7,680	(1,188)	1,436
Changes in assets and liabilities, net of effect of acquisition:
Accounts receivable, net	8,445	4,272	(11,136)
Inventory, net	1,357	128	6,040
Current and other assets	(605)	(5,368)	1,355
Accounts payable	5,407	(62)	(6,311)
Accrued liabilities	4,998	500	(418)
Income taxes	206	119	5,149
Cash provided by operating activities	146,869	154,438	141,491
CASH FLOWS FROM INVESTING ACTIVITIES
Proceeds from sales of investments	102,517	96,129	102,414
Proceeds from maturities of investments	97,164	120,430	137,955
Purchase of investments	(300,620)	(216,013)	(247,355)
Acquisition, net of cash acquired	0	(150)	0
Capital expenditures and other assets	(30,661)	(21,962)	(50,985)
Cash used for investing activities	(131,600)	(21,566)	(57,971)
CASH FLOWS FROM FINANCING ACTIVITIES
Repurchase of common stock	(497,393)	(112,939)	(85,654)
Employees' tax withheld and paid for restricted stock and restricted stock units	(11,068)	(7,611)	(6,222)
Proceeds from issuances under stock-based compensation plans	15,384	23,042	24,055
Payment of cash dividends	(21,061)	(25,730)	(17,372)
Proceeds from revolving line of credit	155,749	34,500	0
Repayments of revolving line of credit	(190,249)	0	0
Proceeds from bonds issuance, net of issuance costs	488,401	0	0
Excess tax benefit from stock-based compensation	3,540	3,520	4,659
Cash used for financing activities	(56,697)	(85,218)	(80,534)
Effect of exchange rate changes on cash and cash equivalents	(156)	(3,508)	942
Net increase (decrease) in cash and cash equivalents	(41,584)	44,146	3,928
Cash and cash equivalents at beginning of year	276,850	232,704	228,776
Cash and cash equivalents at end of year	235,266	276,850	232,704
SUPPLEMENTAL DISCLOSURES
Cash paid for income taxes	25,517	33,804	31,021
Cash paid for interest	12,833	0	0
Non-cash investing activity - purchases of property, plant, and equipment for which payment has not yet been made	$ 0	$ 2,087	$ 0