Consolidated Statements of Shareholders' Equity (USD $) In Thousands, except Share data	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Total
Balance at Dec. 31, 2008	$ 1,348	$ 949,758	$ 1,342,625	$ (11,513)	$ 2,282,218
Balance (in shares) at Dec. 31, 2008	134,829,000
Net income			307,498		307,498
Unrealized loss on cash flow hedge, net of tax				3,551	3,551
Issuance of common stock under employee benefit plans	4	12,969			12,973
Issuance of common stock under employee benefit plans, shares	393,000.0
Net issuance of common stock upon exercise of stock options	23	54,049			54,072
Net issuance of common stock upon exercise of stock options, shares	2,246,000
Excess tax benefit of stock options exercised		9,043			9,043
Share based compensation		14,410			14,410
Fair value of equity component of exchangeable notes		2,100			2,100
Balance at Dec. 31, 2009	1,375	1,042,329	1,650,123	(7,962)	2,685,865
Balance (in shares) at Dec. 31, 2009	137,468,000
Net income			419,373		419,373
Unrealized loss on cash flow hedge, net of tax				4,992	4,992
Issuance of common stock under employee benefit plans	2	7,860			7,862
Issuance of common stock under employee benefit plans, shares	194,000.0
Net issuance of common stock upon exercise of stock options	23	56,827			56,850
Net issuance of common stock upon exercise of stock options, shares	2,332,000
Excess tax benefit of stock options exercised		18,419			18,419
Share based compensation		16,052			16,052
Exchange of exchangeable notes by holders	10	262			272
Exchange of exchangeable notes by holders, shares	1,032,000
Balance at Dec. 31, 2010	1,410	1,141,749	2,069,496	(2,970)	3,209,685
Balance (in shares) at Dec. 31, 2010	141,026,000				141,025,544
Net income			507,673		507,673
Unrealized loss on cash flow hedge, net of tax				2,970	2,970
Issuance of common stock under employee benefit plans	2	9,037			9,039
Issuance of common stock under employee benefit plans, shares	170,000.0
Net issuance of common stock upon exercise of stock options	19	50,290			50,309
Net issuance of common stock upon exercise of stock options, shares	1,861,000
Excess tax benefit of stock options exercised		22,885			22,885
Share based compensation		18,922			18,922
Share repurchases, including fees	(159)	(132,778)	(843,695)		(976,632)
Share repurchases, including fees, shares	(15,877,000)
Balance at Dec. 31, 2011	$ 1,272	$ 1,110,105	$ 1,733,474	$ 0	$ 2,844,851
Balance (in shares) at Dec. 31, 2011	127,180,000				127,179,792