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Share-Based Compensation - Narrative (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2015
Sep. 30, 2014
Sep. 30, 2015
Sep. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Share-based compensation expense $ 3.6 $ 3.1 $ 17.5 $ 18.6
Share-based compensation, capitalized 0.9 $ 1.5 $ 3.2 $ 4.5
Restricted Stock        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period (in years)     4 years  
Unrecognized compensation cost related to unvested awards 21.9   $ 21.9  
Unrecognized compensation cost, period of recognition (in years)     2 years 2 months 12 days  
Performance Unit and Performance Share Units        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period (in years)     3 years  
Vesting Four Years from Grant Date | Restricted Stock Units        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period (in years)     4 years  
Unrecognized compensation cost related to unvested awards 1.8   $ 1.8  
Unrecognized compensation cost, period of recognition (in years)     1 year 9 months 18 days  
Vesting Two Years from Grant Date | Restricted Stock Units        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period (in years)     2 years  
Unrecognized compensation cost related to unvested awards $ 0.2   $ 0.2  
Unrecognized compensation cost, period of recognition (in years)     10 months 24 days  
Percentage vesting at the end of the first year     40.00%  
Percentage vesting at the end of the second year     60.00%  
Discount from common stock price using a credit spread, percentage     7.20%