Consolidated Statement of Shareholders' Equity (USD $)	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss [Member]
Beginning Balance at Dec. 31, 2012	$ 572,285,000	$ 86,000	$ 165,248,000	$ 436,466,000	$ (29,515,000)
Beginning Balance, Shares at Dec. 31, 2012	43,055,000	43,055,000
Issuance of common stock under stock option plans	16,242,000	1,000	16,241,000
Issuance of common stock under stock option plans, shares	710,000	710,000
Repurchase of common stock	(11,891,000)			(11,891,000)
Repurchase of common stock, shares		(268,000)
Stock-based compensation expense	6,079,000		6,079,000
Excess tax benefit from stock option exercises	2,773,000		2,773,000
Tax benefit for research and development credits as a result of stock option accounting	103,000		103,000
Net income	32,403,000			32,403,000
Net unrealized loss on available-for- sale investments, net of tax of $276	(1,106,000)				(1,106,000)
Reclassification of net realized gain on the sale of available-for-sale investments	(83,000)				(83,000)
Foreign currency translation adjustment, net of tax of $181	(1,807,000)				(1,807,000)
Ending Balance at Jun. 30, 2013	$ 614,998,000	$ 87,000	$ 190,444,000	$ 456,978,000	$ (32,511,000)
Ending Balance, Shares at Jun. 30, 2013	43,497,000	43,497,000