Share-Based Compensation (Details 2) (USD $)	6 Months Ended
	Jun. 30, 2012
Restricted stock activity
Restricted shares outstanding, beginning of period	$ 31.89
Restricted shares outstanding, beginning of period, shares	834,703
Restricted shares granted	$ 31.78
Restricted shares granted, shares	514,850
Restricted shares canceled	$ 32.45
Restricted shares canceled, shares	(35,256)
Restricted shares vested	$ 26.23
Restricted shares vested, shares	(349,766)
Restricted shares outstanding, end of period	$ 33.86
Restricted shares outstanding, end of period, shares	964,531