CONSOLIDATED STATEMENT OF SHAREHOLDERS' EQUITY (USD $) In Thousands	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	$ 86	$ 165,248	$ 436,466	$ (29,515)
Beginning Balance, Shares at Dec. 31, 2012	43,055	43,055
Issuance of common stock under stock option plans	9,168	1	9,167
Issuance of common stock under stock option plans, shares	397	397
Stock-based compensation expense	3,298		3,298
Excess tax benefit from stock option exercises	1,376		1,376
Tax benefit for research and development credits as a result of stock option accounting	103		103
Net income	15,583			15,583
Net unrealized gain on available-for-sale investments, net of tax of $42	173				173
Reclassification of net realized gain on the sale of available-for-sale investments	(31)				(31)
Foreign currency translation adjustment, net of tax of $227	(2,494)				(2,494)
Ending Balance at Mar. 31, 2013	$ 599,461	$ 87	$ 179,192	$ 452,049	$ (31,867)
Ending Balance, Shares at Mar. 31, 2013	43,452	43,452