CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Jun. 30, 2014	Jun. 30, 2013
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 28,672	$ 26,953
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	4,624	4,108
Stock-based compensation	6,305	4,988
Provision for excess and obsolete inventories	379	1,783
Deferred income taxes	2,715	5,703
Excess tax benefit from stock-based compensation	(992)	(3,573)
Other operating activities	581	1,065
Changes in assets and liabilities:
Accounts receivable, net	(12,631)	5,916
Inventory, net	(3,983)	228
Current and other assets	(970)	703
Accounts payable	5,995	(4,340)
Accrued liabilities	(4,520)	(7,277)
Income taxes	3,363	(2,117)
Cash provided by operating activities	29,538	34,140
CASH FLOWS FROM INVESTING ACTIVITIES
Proceeds from sales of investments	5,014	30,815
Proceeds from maturities of investments	50,900	35,200
Purchase of investments	(54,867)	(57,121)
Capital expenditures	(7,312)	(13,014)
Cash used for investing activities	(6,265)	(4,120)
CASH FLOWS FROM FINANCING ACTIVITIES
Repurchase of common stock	(12,438)	(10,766)
Proceeds from issuances under stock-based compensation plans	2,832	13,163
Employees' tax withheld and paid for restricted stock and restricted stock units	(5,787)	(4,026)
Payment of cash dividends	(6,389)	(4,368)
Excess tax benefit from stock-based compensation	992	3,573
Cash used for financing activities	(20,790)	(2,424)
Effect of exchange rate changes on cash and cash equivalents	63	(29)
Net increase in cash and cash equivalents	2,546	27,567
Cash and cash equivalents at beginning of period	232,704	228,776
Cash and cash equivalents at end of period	$ 235,250	$ 256,343