Stock-Based Compensation Restricted Stock Units (Details) (USD $) In Millions, except Share data, unless otherwise specified	9 Months Ended
	Sep. 30, 2012
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Incentive shares granted	971,000
Incentive shares outstanding at September 30, 2012	80,356
Share Based Compensation Arrangement by Share Based Payment Award, Options And Ssars, Outstanding, Intrinsic Value	$ 28.8
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost	2.2
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Incentive share awards outstanding at January 1, 2012	1,112,868
Incentive shares granted	329,426
Incentive share awards vested	(407,909)
Incentive share awards cancelled	(56,755)
Incentive shares outstanding at September 30, 2012	977,630
Incentive share awards outstanding Weighted Average Contractual Term (in years)	1.4
Share Based Compensation Arrangement by Share Based Payment Award, Options And Ssars, Outstanding, Intrinsic Value	12.2
Vested and expected to vest at September 30, 2012	928,749
Vested and expected to vest Weighted Average Contractual Term (in years)	0.00
Vested and expected to vest Aggregate Intrinsic Value (in millions)	11.6
Incentive share awards exercisable	0
Incentive share awards exercisable Weighted Average Contractual Term (in years)	0
Incentive share awards exercisable Aggregate Intrinsic Value (in millions)	$ 0