Stock-Based Compensation Restricted Stock Units (Details) (USD $) In Millions, except Share data, unless otherwise specified	9 Months Ended
	Sep. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Incentive shares granted	343,000
Incentive shares ouststanding Aggregate Intrinsic Value (in millions)	$ 37.4
Director restricted stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation Expense	0.2
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation Expense	2.0
Incentive share awards outstanding at January 1, 2012	960,388
Incentive shares granted	158,474
Incentive share awards vested	(346,107)
Incentive share awards cancelled	(478)
Incentive shares outstanding at September 30, 2012	772,277
Incentive share awards outstanding Weighted Average Contractual Term (in years)	1 year 1 month 6 days
Incentive shares ouststanding Aggregate Intrinsic Value (in millions)	13.5
Vested and expected to vest at September 30, 2012	733,663
Vested and expected to vest Weighted Average Contractual Term (in years)	0.00
Vested and expected to vest Aggregate Intrinsic Value (in millions)	12.8
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation Expense	$ 1.3
Incentive shares outstanding at September 30, 2012	459,422
Director [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Incentive share awards outstanding at January 1, 2012	556,987
Incentive shares granted	108,174
Incentive share awards cancelled	(205,739)
Incentive shares outstanding at September 30, 2012	93,179
Chief Executive Officer [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Incentive shares outstanding at September 30, 2012	300,000