CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Jun. 30, 2012	Jun. 30, 2011
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 23,563	$ 26,731
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	3,786	3,462
Stock-based compensation	4,620	4,179
Provision for excess and obsolete inventories	250	322
Deferred income taxes	(1,737)	(2,143)
Income tax benefit associated with stock option exercises	1,299	1,381
Excess tax benefit from stock-based compensation	(140)	(2,570)
Amortization of premium on investments, net	320	431
Other operating activities	252	131
Changes in assets and liabilities:
Accounts receivable, net	4,451	(5,607)
Inventory, net	(5,153)	(1,453)
Current and other assets	(2,681)	(2,421)
Accounts payable	(4,462)	(6,684)
Accrued liabilities	(1,434)	(5,067)
Income taxes	5,262	8,531
Cash provided by operating activities	28,196	19,223
CASH FLOWS FROM INVESTING ACTIVITIES
Proceeds from sales of short-term investments	15,857	62,948
Proceeds from maturities of short-term investments	27,595	38,317
Purchase of short-term investments	(35,062)	(68,077)
Proceeds from sales of long-term investments	0	4,936
Purchase of long-term investments	(8,423)	(35,145)
Capital expenditures and other assets	(16,577)	(3,935)
Cash used for investing activities	(16,610)	(956)
CASH FLOWS FROM FINANCING ACTIVITIES
Repurchase of common stock	(16,473)	(90,668)
Equity forward contract related to accelerated share repurchase program	0	(18,872)
Proceeds from issuance of common stock	1,319	11,515
Proceeds from revolving line of credit	18,000	0
Repayments of revolving line of credit	(13,000)	0
Payment of cash dividends	(4,247)	(2,427)
Employees' tax withheld and paid for restricted stock and restricted stock units	(1,290)	(705)
Excess tax benefit from stock-based compensation	140	2,570
Cash used for financing activities	(15,551)	(98,587)
Effect of exchange rate changes on cash and cash equivalents	(731)	673
Net decrease in cash and cash equivalents	(4,696)	(79,647)
Cash and cash equivalents at beginning of period	209,335	277,373
Cash and cash equivalents at end of period	$ 204,639	$ 197,726