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Share-Based Compensation - Narrative (Details) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2015
Jun. 30, 2014
Jun. 30, 2015
Jun. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Share-based compensation expense $ 8.2 $ 7.3 $ 13.9 $ 15.5
Share-based compensation, capitalized 1.3 $ 1.9 $ 2.6 $ 3.1
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 25.0   $ 25.0  
Unrecognized compensation cost, period of recognition (in years)     2 years  
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 5.4   $ 5.4  
Unrecognized compensation cost, period of recognition (in years)     2 years 1 month  
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 $ 1.0   $ 1.0  
Unrecognized compensation cost, period of recognition (in years)     1 year 1 month  
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     3.60%