Consolidated Statements of Changes in Equity (USD $) In Thousands, unless otherwise specified	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]	Noncontrolling Interest [Member]	Parent [Member]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, beginning of period at Dec. 31, 2008		$ 5	$ 8,811,497	$ (4,245)	$ (2,905,852)	$ 0	$ 5,901,405
Shares, Issued at Dec. 31, 2008		526,752
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Consolidated net income	115,228				116,999	(1,771)	115,228
Change in net unrealized (loss) gain on investments, net	(2,800)			(2,757)			(2,757)
Change in foreign currency translation adjustment, net	5,600			5,569			5,569
Consolidated comprehensive income	118,000						118,040
Purchase Of Subsidiary Shares By Noncontrolling Interest						4,400	4,400
Stock Issued During Period, Shares, Employee Stock Purchase Plans	3,200	3,221
Stock Issued During Period, Value, Employee Stock Purchase Plan			39,164				39,164
Stock Issued During Period, Shares, Restricted Stock Award, Gross		1,432
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period	8,600	8,651
Stock Issued During Period, Value, Stock Options Exercised			126,284				126,284
Stock Repurchased and Retired During Period, Shares		(20,715)
Stock Repurchased and Retired During Period, Value			(6,216)		(447,672)		(453,888)
Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition, Value			139,659				139,659
Adjustments to Additional Paid in Capital, Tax Effect from Share-based Compensation			(50,299)				(50,299)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, end of period at Dec. 31, 2009		5	9,060,089	(1,433)	(3,236,525)	2,629	5,824,765
Shares, Issued at Dec. 31, 2009		519,341
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Consolidated net income	619,373				618,402	(971)	619,373
Change in net unrealized (loss) gain on investments, net	(300)			(317)			(317)
Change in foreign currency translation adjustment, net	500			499			499
Consolidated comprehensive income	619,600						619,555
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders						(3,000)	(3,000)
Stock Issued During Period, Shares, Employee Stock Purchase Plans	2,000	1,974
Stock Issued During Period, Value, Employee Stock Purchase Plan			41,829				41,829
Stock Issued During Period, Shares, Restricted Stock Award, Gross		2,224
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period	21,600	21,568
Stock Issued During Period, Value, Stock Options Exercised			409,395				409,395
Value Shares Assumed In Connection With Business Acquisition			2,355				2,355
Stock Repurchased and Retired During Period, Shares	(19,700)	(19,654)
Stock Repurchased and Retired During Period, Value	(563,500)		(75,242)		(488,284)		(563,526)
Stock Repurchased and Retired During Period Net of Issuances Shares		(75)
Shares Repuchased And Retired Related To Net Issuances	(1,900)		(17)		(1,930)		(1,947)
Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition, Value			177,825				177,825
Adjustments to Additional Paid in Capital, Tax Effect from Share-based Compensation			101,549				101,549
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, end of period at Dec. 31, 2010	6,608,800	5	9,717,783	(1,251)	(3,108,337)	600	6,608,800
Shares, Issued at Dec. 31, 2010		525,378
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Consolidated net income	425,012				425,136	(124)	425,012
Change in net unrealized (loss) gain on investments, net	(9,900)			(9,980)			(9,980)
Change in foreign currency translation adjustment, net	(6,400)			(6,359)			(6,359)
Consolidated comprehensive income	408,700						408,673
Stock Issued During Period, Shares, Employee Stock Purchase Plans	2,400	2,400
Stock Issued During Period, Value, Employee Stock Purchase Plan			51,687				51,687
Stock Issued During Period, Shares, Restricted Stock Award, Gross		2,431
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period	13,900	13,904
Stock Issued During Period, Value, Stock Options Exercised			293,856				293,856
Stock Repurchased and Retired During Period, Shares	(17,500)	(17,500)
Stock Repurchased and Retired During Period, Value	(541,200)		(256,372)		(284,866)		(541,238)
Stock Repurchased and Retired During Period Net of Issuances Shares		(204)
Shares Repuchased And Retired Related To Net Issuances	(7,400)		(3,017)		(4,335)		(7,352)
Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition, Value			217,761				217,761
Adjustments to Additional Paid in Capital, Tax Effect from Share-based Compensation			57,471				57,471
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, end of period at Dec. 31, 2011	$ 7,089,658	$ 5	$ 10,079,169	$ (17,590)	$ (2,972,402)	$ 476	$ 7,089,658
Shares, Issued at Dec. 31, 2011		526,409