CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 112,417	$ 106,402	$ 109,036
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	15,566	16,219	13,760
Stock-based compensation	23,180	18,350	17,481
Provision for excess and obsolete inventories	4,138	1,576	2,222
Deferred income taxes	(5,813)	984	(3,497)
Excess tax benefit from stock-based compensation	(4,659)	(2,722)	(7,043)
Other operating activities	1,983	2,249	2,995
Changes in assets and liabilities, net of effect of acquisition:
Accounts receivable, net	(11,136)	(16,335)	(9,402)
Inventory, net	6,040	(14,811)	606
Current and other assets	1,355	(6,056)	(67)
Accounts payable	(6,311)	2,778	131
Accrued liabilities	(418)	9,641	(4,303)
Income taxes	5,149	7,226	18,529
Cash provided by operating activities	141,491	125,501	140,448
CASH FLOWS FROM INVESTING ACTIVITIES
Proceeds from sales of investments	102,414	56,471	88,489
Proceeds from maturities of investments	137,955	184,115	189,131
Purchase of investments	(247,355)	(258,278)	(267,895)
Capital expenditures and other assets	(50,985)	(39,310)	(19,140)
Acquisition, net of cash acquired	0	(1,926)	0
Cash used for investing activities	(57,971)	(58,928)	(9,415)
CASH FLOWS FROM FINANCING ACTIVITIES
Repurchase of common stock	(85,654)	(23,931)	(273,791)
Proceeds from issuances under stock-based compensation plans	24,055	31,865	43,123
Employees' tax withheld and paid for restricted stock and restricted stock units	(6,222)	(3,047)	(2,596)
Proceeds from revolving line of credit	0	18,000	68,500
Repayments of revolving line of credit	0	(55,000)	(31,500)
Payment of cash dividends	(17,372)	(17,072)	(9,040)
Excess tax benefit from stock-based compensation	4,659	2,722	7,043
Cash used for financing activities	(80,534)	(46,463)	(198,261)
Effect of exchange rate changes on cash and cash equivalents	942	(669)	(810)
Net increase (decrease) in cash and cash equivalents	3,928	19,441	(68,038)
Cash and cash equivalents at beginning of year	228,776	209,335	277,373
Cash and cash equivalents at end of year	232,704	228,776	209,335
SUPPLEMENTAL DISCLOSURES
Cash paid for income taxes	$ 31,021	$ 29,953	$ 20,752