CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 84,474	$ 77,693
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	11,671	12,104
Stock-based compensation	16,996	14,173
Provision for excess and obsolete inventories	4,419	1,306
Deferred income taxes	530	(1,030)
Excess tax benefit from stock-based compensation	(4,434)	(930)
Other operating activities	1,345	1,639
Changes in assets and liabilities:
Accounts receivable, net	(6,539)	(1,215)
Inventory, net	(3,135)	(13,943)
Current and other assets	826	(4,928)
Accounts payable	(10,339)	1,723
Accrued liabilities	1,388	3,840
Income taxes	(5,080)	2,822
Cash provided by operating activities	92,122	93,254
CASH FLOWS FROM INVESTING ACTIVITIES
Proceeds from sales of investments	89,682	38,078
Proceeds from maturities of investments	95,210	117,665
Purchase of investments	(181,836)	(188,062)
Acquisitions, net of cash acquired	0	(1,926)
Capital expenditures	(37,657)	(29,378)
Cash used for investing activities	(34,601)	(63,623)
CASH FLOWS FROM FINANCING ACTIVITIES
Repurchase of common stock	(56,754)	(23,626)
Proceeds from issuances under stock-based compensation plans	19,599	13,091
Employees' tax withheld and paid for restricted stock and restricted stock units	(6,014)	(2,848)
Proceeds from revolving line of credit	0	18,000
Repayments of revolving line of credit	0	(35,000)
Payment of cash dividends	(13,105)	(12,756)
Excess tax benefit from stock-based compensation	4,434	930
Cash used for financing activities	(51,840)	(42,209)
Effect of exchange rate changes on cash and cash equivalents	1,077	(101)
Net increase (decrease) in cash and cash equivalents	6,758	(12,679)
Cash and cash equivalents at beginning of period	228,776	209,335
Cash and cash equivalents at end of period	$ 235,534	$ 196,656