Stock-Based Compensation Restricted Stock Units (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Incentive shares granted	343,000
Incentive shares outstanding at September 30, 2012	77,533
Incentive shares ouststanding Aggregate Intrinsic Value (in millions)	$ 57.4
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Incentive share awards outstanding at January 1, 2012	960,388
Incentive shares granted	123,286
Incentive share awards vested	(341,607)
Incentive share awards cancelled	(478)
Incentive shares outstanding at September 30, 2012	741,589
Incentive share awards outstanding Weighted Average Contractual Term (in years)	1 year 7 months 6 days
Incentive shares ouststanding Aggregate Intrinsic Value (in millions)	16.0
Vested and expected to vest at September 30, 2012	704,510
Vested and expected to vest Weighted Average Contractual Term (in years)	0.00
Vested and expected to vest Aggregate Intrinsic Value (in millions)	15.2
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