Share-Based Compensation (Details 2) (USD $)	3 Months Ended
	Mar. 31, 2012
Restricted stock activity
Restricted shares outstanding, beginning of period	$ 31.89
Restricted shares outstanding, beginning of period, shares	834,703
Restricted shares granted	$ 32.62
Restricted shares granted, shares	474,200
Restricted shares canceled	$ 32.33
Restricted shares canceled, shares	(9,053)
Restricted shares vested	$ 26.73
Restricted shares vested, shares	(309,816)
Restricted shares outstanding, end of period	$ 33.85
Restricted shares outstanding, end of period, shares	990,034