Stock-Based Compensation Restricted Stock Units (Details) (USD $) In Millions, except Share data, unless otherwise specified	6 Months Ended
	Jun. 30, 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 ouststanding Aggregate Intrinsic Value (in millions)	$ 25.5
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	155,974
Incentive share awards vested	(341,607)
Incentive share awards cancelled	(478)
Incentive shares outstanding at September 30, 2012	774,277
Incentive share awards outstanding Weighted Average Contractual Term (in years)	1 year 4 months 24 days
Incentive shares ouststanding Aggregate Intrinsic Value (in millions)	11.5
Vested and expected to vest at September 30, 2012	735,563
Vested and expected to vest Weighted Average Contractual Term (in years)	0.00
Vested and expected to vest Aggregate Intrinsic Value (in millions)	$ 10.9