CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 26,953	$ 23,563
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	4,108	3,786
Stock-based compensation	4,988	4,620
Provision for excess and obsolete inventories	1,783	250
Deferred income taxes	5,703	(438)
Excess tax benefit from stock-based compensation	(3,573)	(140)
Amortization of premium on investments, net	227	320
Non-cash charges for restructuring and other related items	723	0
Other operating activities	115	252
Changes in assets and liabilities:
Accounts receivable, net	5,916	4,451
Inventory, net	228	(5,153)
Current and other assets	703	(2,681)
Accounts payable	(4,340)	(4,462)
Accrued liabilities	(7,277)	(1,434)
Income taxes	(2,117)	5,262
Cash provided by operating activities	34,140	28,196
CASH FLOWS FROM INVESTING ACTIVITIES
Proceeds from sales of short-term investments	26,031	15,857
Proceeds from maturities of short-term investments	35,200	27,595
Purchase of short-term investments	(34,015)	(35,062)
Proceeds from sales of long-term investments	4,784	0
Purchase of long-term investments	(23,106)	(8,423)
Capital expenditures	(13,014)	(16,577)
Cash used for investing activities	(4,120)	(16,610)
CASH FLOWS FROM FINANCING ACTIVITIES
Repurchase of common stock	(10,766)	(16,473)
Proceeds from issuances under stock-based compensation plans	13,163	1,319
Employees' tax withheld and paid for restricted stock and restricted stock units	(4,026)	(1,290)
Proceeds from revolving line of credit	0	18,000
Repayments of revolving line of credit	0	(13,000)
Payment of cash dividends	(4,368)	(4,247)
Excess tax benefit from stock-based compensation	3,573	140
Cash used for financing activities	(2,424)	(15,551)
Effect of exchange rate changes on cash and cash equivalents	(29)	(731)
Net increase (decrease) in cash and cash equivalents	27,567	(4,696)
Cash and cash equivalents at beginning of period	228,776	209,335
Cash and cash equivalents at end of period	256,343	204,639
Property, plant, and equipment purchases unpaid and included in accounts payable	2,709	1,619
Transfers from long-term investments to short-term investments	$ 12,615	$ 34,507