CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 77,693	$ 85,150
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	12,104	10,328
Stock-based compensation	14,173	13,267
Provision for excess and obsolete inventories	1,306	2,337
Deferred income taxes	(1,030)	(3,755)
Excess tax benefit from stock-based compensation	(930)	(5,147)
Amortization of premium on investments, net	858	1,228
Other operating activities	781	627
Changes in assets and liabilities, net of effect of acquisition:
Accounts receivable, net	(1,215)	(6,378)
Inventory, net	(13,943)	(3,599)
Current and other assets	(4,928)	1,093
Accounts payable	1,723	(12,345)
Accrued liabilities	3,840	(7,235)
Income taxes	2,822	11,900
Cash provided by operating activities	93,254	87,471
CASH FLOWS FROM INVESTING ACTIVITIES
Proceeds from sales of short-term investments	28,087	68,539
Proceeds from maturities of short-term investments	117,665	126,231
Purchase of short-term investments	(97,599)	(122,480)
Proceeds from sales of long-term investments	9,991	4,936
Purchase of long-term investments	(90,463)	(68,313)
Acquisition, net of cash acquired	(1,926)	0
Capital expenditures and other assets	(29,378)	(15,042)
Cash used for investing activities	(63,623)	(6,129)
CASH FLOWS FROM FINANCING ACTIVITIES
Repurchase of common stock	(23,626)	(229,121)
Equity forward contract related to accelerated share repurchase program	0	(15,000)
Proceeds from sale of treasury stock	2,485	2,519
Proceeds from issuance of common stock	10,606	27,072
Proceeds from revolving line of credit	18,000	53,500
Repayments of revolving line of credit	(35,000)	(14,000)
Payment of cash dividends	(12,756)	(6,884)
Employees' tax withheld and paid for restricted stock and restricted stock units	(2,848)	(2,457)
Excess tax benefit from stock-based compensation	930	5,147
Cash used for financing activities	(42,209)	(179,224)
Effect of exchange rate changes on cash and cash equivalents	(101)	(1,428)
Net decrease in cash and cash equivalents	(12,679)	(99,310)
Cash and cash equivalents at beginning of period	209,335	277,373
Cash and cash equivalents at end of period	196,656	178,063
Property, plant and equipment purchases unpaid and included in accounts payable	1,376	0
Transfer from Investments	$ 56,466	$ 40,374