CONSOLIDATED STATEMENTS OF SHAREHOLDERS EQUITY - USD ($) shares in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss [Member]
Beginning Balance at Dec. 31, 2013	$ 643,912,000	$ 174,000	$ 211,440,000	$ 462,131,000	$ (29,833,000)
Beginning Balance, Shares at Dec. 31, 2013		86,831
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under stock option plans	16,930,000	$ 2,000	16,928,000
Issuance of common stock under stock option plans, shares		1,245
Repurchase of common stock	(59,673,000)	$ 3,000		(59,670,000)
Repurchase of common stock, shares		(1,534)
Stock-based compensation expense	15,158,000		15,158,000
Excess tax benefit from stock option exercises	7,871,000		7,871,000
Tax benefit for research and development credits as a result of stock options	320,000		320,000
Net income	121,485,000			121,485,000
Net unrealized gain (loss) on cash flow hedges, net of tax	(118,000)				(118,000)
Reclassification of net realized (gain) loss into current operations	46,000				46,000
Net unrealized gain (loss) on available-for-sale investments, net of tax	579,000				579,000
Reclassification of net realized gain on the sale of available-for-sale investments	(673,000)				(673,000)
Foreign currency translation adjustments, net of tax	(9,400,000)				(9,400,000)
Balance at Dec. 31, 2014	736,437,000	$ 173,000	251,717,000	523,946,000	(39,399,000)
Balance, Shares at Dec. 31, 2014		86,542
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under stock option plans	27,582,000	$ 3,000	27,579,000
Issuance of common stock under stock option plans, shares		1,520
Repurchase of common stock	(126,351,000)	$ (6,000)		(126,345,000)
Repurchase of common stock, shares		(3,206)
Stock-based compensation expense	21,274,000		21,274,000
Excess tax benefit from stock option exercises	9,964,000		9,964,000
Tax benefit for research and development credits as a result of stock options	474,000		474,000
Payment of dividends	(18,062,000)			(18,062,000)
Net income	187,074,000			187,074,000
Net unrealized gain (loss) on cash flow hedges, net of tax	(27,000)				(27,000)
Reclassification of net realized (gain) loss into current operations	201,000				201,000
Net unrealized gain (loss) on available-for-sale investments, net of tax	(939,000)				(939,000)
Reclassification of net realized gain on the sale of available-for-sale investments	(344,000)				(344,000)
Foreign currency translation adjustments, net of tax	(11,616,000)				(11,616,000)
Balance at Dec. 31, 2015	$ 825,667,000	$ 170,000	311,008,000	566,613,000	(52,124,000)
Balance, Shares at Dec. 31, 2015	84,856	84,856
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under stock option plans	$ 43,468,000	$ 4,000	43,464,000
Issuance of common stock under stock option plans, shares	1,977	1,977
Repurchase of common stock	$ (47,149,000)	$ (2,000)		(47,147,000)
Repurchase of common stock, shares		(894)
Stock-based compensation expense	20,558,000		20,558,000
Payment of dividends	(25,213,000)			(25,213,000)
Net income	149,572,000			149,572,000
Net unrealized gain (loss) on cash flow hedges, net of tax	(567,000)				(567,000)
Reclassification of net realized (gain) loss into current operations	398,000				398,000
Net unrealized gain (loss) on available-for-sale investments, net of tax	1,672,000				1,672,000
Reclassification of net realized gain on the sale of available-for-sale investments	(191,000)				(191,000)
Foreign currency translation adjustments, net of tax	(5,616,000)				(5,616,000)
Balance at Dec. 31, 2016	$ 962,599,000	$ 172,000	$ 375,030,000	$ 643,825,000	$ (56,428,000)
Balance, Shares at Dec. 31, 2016	85,939	85,939