CONSOLIDATED STATEMENTS OF SHAREHOLDERS EQUITY (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss [Member]
Beginning Balance at Dec. 31, 2011	$ 552,980	$ 168	$ 135,584	$ 434,581	$ (17,353)
Beginning Balance, Shares at Dec. 31, 2011		84,446,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under stock option plans	17,468	4	17,464
Issuance of common stock under stock option plans, shares		1,664,000
Stock-based compensation expense	8,520		8,520
Excess tax benefit from stock option exercises	3,594		3,594
Payment of dividends	(66,213)			(66,213)
Net income	68,098			68,098
Net unrealized gain (loss) on cash flow hedges, net of tax	0
Reclassification of net realized (gain) loss into current operations	0
Net unrealized gain (loss) on available-for-sale investments, net of tax	2,079				2,079
Reclassification of net realized gain on the sale of available-for-sale investments	(1,695)				(1,695)
Foreign currency translation adjustments, net of tax	(12,546)				(12,546)
Balance at Dec. 31, 2012	572,285	172	165,162	436,466	(29,515)
Balance, Shares at Dec. 31, 2012		86,110,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under stock option plans	27,792	2	27,790
Issuance of common stock under stock option plans, shares		2,440,000
Repurchase of common stock	(47,908)			(47,908)
Repurchase of common stock, shares		(1,719,000)
Stock-based compensation expense	10,620		10,620
Excess tax benefit from stock option exercises	7,658		7,658
Tax benefit for research and development credits as a result of stock options	210		210
Net income	73,573			73,573
Net unrealized gain (loss) on cash flow hedges, net of tax	104				104
Reclassification of net realized (gain) loss into current operations	0
Net unrealized gain (loss) on available-for-sale investments, net of tax	(190)				(190)
Reclassification of net realized gain on the sale of available-for-sale investments	(314)				(314)
Foreign currency translation adjustments, net of tax	82				82
Balance at Dec. 31, 2013	643,912	174	211,440	462,131	(29,833)
Balance, Shares at Dec. 31, 2013	86,831,000	86,831,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under stock option plans	16,930	2	16,928
Issuance of common stock under stock option plans, shares	1,232,000	1,245,000
Repurchase of common stock	(59,673)	(3)		(59,670)
Repurchase of common stock, shares		(1,534,000)
Stock-based compensation expense	15,158		15,158
Excess tax benefit from stock option exercises	7,871		7,871
Tax benefit for research and development credits as a result of stock options	320		320
Net income	121,485			121,485
Net unrealized gain (loss) on cash flow hedges, net of tax	(118)				(118)
Reclassification of net realized (gain) loss into current operations	46				46
Net unrealized gain (loss) on available-for-sale investments, net of tax	579				579
Reclassification of net realized gain on the sale of available-for-sale investments	(673)				(673)
Foreign currency translation adjustments, net of tax	(9,400)				(9,400)
Balance at Dec. 31, 2014	$ 736,437	$ 173	$ 251,717	$ 523,946	$ (39,399)
Balance, Shares at Dec. 31, 2014	86,542,000	86,542,000