Stock-based Compensation (Summary of Restricted Stock Awards Activity) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted, number of shares	900	1,100	2,200
Shares granted, weighted-average grant-date fair value (in dollars per share)	$ 37.05	$ 31.13	$ 10.08
Restricted Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares outstanding at the beginning of the year, number of shares	4,297
Shares outstanding at the beginning of the year, weighted-average grant-date fair value (in dollars per share)	$ 20.2
Shares granted, number of shares	886
Shares granted, weighted-average grant-date fair value (in dollars per share)	$ 37.1
Shares vested, number of shares	(1,717)
Shares vested, weighted-average grant-date fair value (in dollars per share)	$ 27.3
Shares forfeited, number of shares	(63)
Shares forfeited, weighted-average grant-date fair value (in dollars per share)	$ 19.4
Shares outstanding at the end of year, number of shares	3,403
Shares outstanding at the end of the year, weighted-average grant-date fair value (in dollars per share)	$ 21.1