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Capital - Incentive and Share-based Compensation (Details)
$ / shares in Units, $ in Millions
1 Months Ended 12 Months Ended
May 31, 2017
USD ($)
shares
Mar. 31, 2017
USD ($)
vesting_installment
shares
Jun. 30, 2016
USD ($)
shares
Feb. 29, 2016
USD ($)
vesting_installment
shares
Dec. 31, 2017
USD ($)
$ / shares
shares
Dec. 31, 2016
USD ($)
$ / shares
Dec. 31, 2015
USD ($)
$ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Expected volatility rate look-back period (in years)         6 years    
Weighted-average per unit or share fair value (in dollars per share) | $ / shares         $ 13.77    
Age of grantee at which LTIP unit and restricted stock awards immediately vest         60 years    
Period of service, upon completion of which, grantee's LTIP unit and restricted stock awards will immediately vest         10 years    
Awards that Meet Age and Service Requirements for Vesting [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Noncash share-based compensation expense recognized         $ 1.0 $ 0.7 $ 0.5
Unrecognized compensation expense         $ 0.8    
Unrecognized compensation expense, period for recognition (in years)         1 year 13 months 36 days    
Awards that Do Not Meet Age and Service Requirements for Vesting [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Noncash share-based compensation expense recognized         $ 13.1 9.0 5.0
Unrecognized compensation expense         $ 23.2    
Unrecognized compensation expense, period for recognition (in years)         2 years 4 months 6 days    
Long-Term Incentive Plan Units and Restricted Stock [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Fair value of share-based awards granted in period         $ 19.4 $ 18.4  
Weighted-average per unit or share fair value (in dollars per share) | $ / shares           $ 9.60  
Risk free interest rate         1.55%    
Expected volatility rate         20.00%    
Fair value vested in period         $ 7.6 $ 5.1 3.5
Long-Term Incentive Plan Unit [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Number of shares granted (in shares) | shares         1,372,574    
Time Based Long-Tern Incentive Plan Unit [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Number of shares granted (in shares) | shares   47,993   47,168      
Fair value of share-based awards granted in period   $ 1.6   $ 1.4   $ 0.1  
Performance Based Long-Term Incentive Plan Unit [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Number of shares granted (in shares) | shares   95,156   112,925      
Fair value of share-based awards granted in period   $ 1.0   $ 0.8      
Restricted Stock [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Number of shares granted (in shares) | shares         34,407    
Time Restricted Shares [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Number of shares granted (in shares) | shares   34,407   44,198      
Long-Term Incentive Plan Unit and Restricted Stock [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Fair value of share-based awards granted in period             $ 6.6
Weighted-average per unit or share fair value (in dollars per share) | $ / shares         $ 13.77   $ 13.36
Expected term         2 years 9 months 8 days 2 years 9 months 8 days  
Share-based compensation arrangement by share-based payment award, fair value assumptions, expected dividend rate         2.05% 2.10% 1.90%
Risk free interest rate           0.84%  
Expected volatility rate           24.00%  
Director [Member] | Time Based Long-Tern Incentive Plan Unit [Member] | 2013 Plan Units Granted In May 2017 [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Number of shares granted (in shares) | shares 50,408            
Fair value of share-based awards granted in period $ 1.0            
Award vesting period (in years) 3 years            
Director [Member] | Time Based Long-Tern Incentive Plan Unit [Member] | 2013 Plan Units Vesting June 2019 [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Number of shares granted (in shares) | shares     43,257        
Fair value of share-based awards granted in period     $ 0.8        
Award vesting period (in years)     3 years        
Executive Officer [Member] | Time Based Long-Tern Incentive Plan Unit [Member] | 2013 Plan Units, Granted in March 2017 [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Number of shares granted (in shares) | shares   313,275          
Fair value of share-based awards granted in period   $ 6.1          
Award vesting period (in years)   4 years          
Number of vesting installments (vesting installments) | vesting_installment   3          
Executive Officer [Member] | Time Based Long-Tern Incentive Plan Unit [Member] | 2013 Plan Units Vesting February 2020 [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Number of shares granted (in shares) | shares       368,225      
Fair value of share-based awards granted in period       $ 5.6      
Award vesting period (in years)       4 years      
Number of vesting installments (vesting installments) | vesting_installment       3      
Executive Officer [Member] | Time Based Long-Tern Incentive Plan Unit [Member] | 2013 Plan Units Vesting February 2021 [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Number of shares granted (in shares) | shares       62,814      
Fair value of share-based awards granted in period       $ 1.0      
Award vesting percentage after three years       30.00%      
Award vesting percentage after four years       30.00%      
Award vesting percentage after five years       40.00%      
Executive Officer [Member] | Performance Based Long-Term Incentive Plan Unit [Member] | 2013 Plan Units, Granted in March 2017 [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Number of shares granted (in shares) | shares   865,742          
Fair value of share-based awards granted in period   $ 9.6          
Award vesting period (in years)   3 years          
Number of vesting installments (vesting installments) | vesting_installment   2          
Executive Officer [Member] | Performance Based Long-Term Incentive Plan Unit [Member] | 2013 Plan Units Vesting February 2020 [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Number of shares granted (in shares) | shares       1,230,228      
Fair value of share-based awards granted in period       $ 8.8      
Award vesting period (in years)       3 years      
Number of vesting installments (vesting installments) | vesting_installment       2      
2013 Plan [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Number of shares authorized under the plan (in shares) | shares         12,200,000    
Number of shares that remain available for future issuance (in shares) | shares         7,000,000    
Maximum [Member] | Long-Term Incentive Plan Unit and Restricted Stock [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Expected term             3 years
Risk free interest rate             1.00%
Expected volatility rate             29.00%
Minimum [Member] | Long-Term Incentive Plan Unit and Restricted Stock [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Expected term             2 years 10 months 24 days
Risk free interest rate             0.80%
Expected volatility rate             24.00%