CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (USD $) In Thousands, unless otherwise specified	Total	Common stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury stock
Balance at Dec. 31, 2009	$ 584,953	$ 973	$ 136,553	$ 670,396	$ (4,667)	$ (218,302)
Balance (in shares) at Dec. 31, 2009		194,570				(18,252)
Increase (Decrease) in Stockholders' Equity
Stock-based compensation	16,810		16,810
Exercise of stock options	20,824	15	20,809
Exercise of stock options (in shares)		2,892
Excess tax benefits from share based payment arrangements	12,374		12,374
Repurchase of common stock	(23,540)					(23,540)
Repurchase of common stock (in shares)						(1,250)
Foreign currency translation	1,837				1,837
Change in unrealized gain on available-for-sale securities, net of tax	3,111				3,111
Net income	212,029			212,029
Balance at Dec. 31, 2010	828,398	988	186,546	882,425	281	(241,842)
Balance (in shares) at Dec. 31, 2010		197,462				(19,502)
Increase (Decrease) in Stockholders' Equity
Stock-based compensation	18,619		18,619
Exercise of stock options	20,318	6	20,312
Exercise of stock options (in shares)		1,181
Issuance of restricted stock (in shares)		86
Excess tax benefits from share based payment arrangements	3,824		3,824
Repurchase of common stock	(176,392)					(176,392)
Repurchase of common stock (in shares)						(4,950)
Foreign currency translation	(3,306)				(3,306)
Change in unrealized gain on available-for-sale securities, net of tax	1,478				1,478
Net income	286,219			286,219
Balance at Dec. 31, 2011	979,158	994	229,301	1,168,644	(1,547)	(418,234)
Balance (in shares) at Dec. 31, 2011		198,729				(24,452)
Increase (Decrease) in Stockholders' Equity
Stock-based compensation	28,007		28,007
Exercise of stock options	11,014	25	10,989
Exercise of stock options (in shares)		5,030
Excess tax benefits from share based payment arrangements	19,656		19,656
Repurchase of common stock	(737,079)					(737,079)
Repurchase of common stock (in shares)						(13,531)
Foreign currency translation	2,096				2,096
Change in unrealized gain on available-for-sale securities, net of tax	1,525				1,525
Net income	340,020			340,020
Balance at Dec. 31, 2012	$ 644,397	$ 1,019	$ 287,953	$ 1,508,664	$ 2,074	$ (1,155,313)
Balance (in shares) at Dec. 31, 2012		203,759				(37,983)