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Capital - Incentive and Share-based Compensation (Details)
$ / shares in Units, $ in Millions
1 Months Ended 12 Months Ended
May 31, 2018
USD ($)
shares
Mar. 31, 2018
USD ($)
vesting_installment
shares
Feb. 28, 2018
USD ($)
vesting_installment
shares
May 31, 2017
USD ($)
shares
Mar. 31, 2017
USD ($)
vesting_installment
shares
Dec. 31, 2018
USD ($)
$ / shares
shares
Dec. 31, 2017
USD ($)
$ / shares
Dec. 31, 2016
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           $ 8.54    
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 Do Not Meet Age and Service Requirements for Vesting                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Noncash share-based compensation expense recognized | $           $ 17.0 $ 13.1 $ 9.0
Unrecognized compensation expense | $           $ 27.4    
Unrecognized compensation expense, period for recognition (in years)           2 years 2 months    
Awards that Meet Age and Service Requirements for Vesting                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Noncash share-based compensation expense recognized | $           $ 1.8 1.0 0.7
Unrecognized compensation expense | $           $ 1.0    
Unrecognized compensation expense, period for recognition (in years)           1 year 13 months 12 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 | $           $ 23.6 $ 19.4  
Weighted-average per unit or share fair value (in dollars per share) | $ / shares             $ 13.77  
Risk free interest rate           2.50%    
Expected volatility rate           20.00%    
Fair value vested in period | $           $ 7.7 $ 7.6 5.1
Long-Term Incentive Plan Unit                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Number of shares granted (in shares)           2,719,801    
Time Based Long-Tern Incentive Plan Unit                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Number of shares granted (in shares)         47,993      
Fair value of share-based awards granted in period | $         $ 1.6      
Time Based Long-Tern Incentive Plan Unit | 2013 Plan Units, Granted in March 2018                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Number of shares granted (in shares)   67,449            
Fair value of share-based awards granted in period | $   $ 1.7            
Award vesting period (in years)   4 years            
Number of vesting installments (vesting installments) | vesting_installment   3            
Performance Based Long-Term Incentive Plan Unit                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Number of shares granted (in shares)         95,156      
Fair value of share-based awards granted in period | $         $ 1.0      
Performance Based Long-Term Incentive Plan Unit | 2013 Plan Units, Granted in March 2018                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Number of shares granted (in shares)   223,950            
Fair value of share-based awards granted in period | $   $ 1.1            
Award vesting period (in years)   3 years            
Number of vesting installments (vesting installments) | vesting_installment   2            
Restricted Stock                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Number of shares granted (in shares)           39,608    
Time Restricted Shares                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Number of shares granted (in shares)         34,407      
Time Restricted Shares | 2013 Plan Units, Granted in March 2018                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Number of shares granted (in shares)   39,608            
Long-Term Incentive Plan Unit and Restricted Stock                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Fair value of share-based awards granted in period | $               $ 18.4
Weighted-average per unit or share fair value (in dollars per share) | $ / shares           $ 8.54   $ 9.60
Expected term           2 years 9 months 12 days 2 years 9 months 8 days  
Share-based compensation arrangement by share-based payment award, fair value assumptions, expected dividend rate           2.30% 2.05% 2.10%
Risk free interest rate             1.55%  
Expected volatility rate             20.00%  
Director | Time Based Long-Tern Incentive Plan Unit                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Number of shares granted (in shares) 65,000              
Fair value of share-based awards granted in period | $ $ 1.0              
Award vesting period (in years) 3 years              
Director | Time Based Long-Tern Incentive Plan Unit | 2013 Plan Units Granted In May 2017                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Number of shares granted (in shares)       50,408        
Fair value of share-based awards granted in period | $       $ 1.0        
Award vesting period (in years)       3 years        
Executive Officer | Time Based Long-Tern Incentive Plan Unit | 2013 Plan Units, Granted in March 2018                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Number of shares granted (in shares)   386,876            
Executive Officer | Time Based Long-Tern Incentive Plan Unit | 2013 Plan Units, Granted in February 2018                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Number of shares granted (in shares)     238,609          
Fair value of share-based awards granted in period | $     $ 4.0          
Award vesting period (in years)             3 years  
Award vesting percentage of award face amount (in percentage)             125.00%  
Executive Officer | Time Based Long-Tern Incentive Plan Unit | 2013 Plan Units, Granted in March 2017                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Number of shares granted (in 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 | Time Based Long-Tern Incentive Plan Unit | Vest immediately                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Number of shares granted (in shares)     25,158          
Executive Officer | Time Based Long-Tern Incentive Plan Unit | Vest over three years                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Number of shares granted (in shares)     213,451          
Award vesting period (in years)     3 years          
Executive Officer | Time Based Long-Tern Incentive Plan Unit | Vest in two equal installments                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Number of vesting installments (vesting installments) | vesting_installment     2          
Executive Officer | Performance Based Long-Term Incentive Plan Unit | 2013 Plan Units, Granted in March 2018                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Number of shares granted (in shares)   1,737,917            
Executive Officer | Performance Based Long-Term Incentive Plan Unit | 2013 Plan Units, Granted in March 2017                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Number of shares granted (in 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      
2013 Plan                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Number of shares authorized under the plan (in shares)           12,200,000    
Number of shares that remain available for future issuance (in shares)           4,300,000    
Maximum | Long-Term Incentive Plan Unit and Restricted Stock                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Risk free interest rate               0.84%
Minimum | Long-Term Incentive Plan Unit and Restricted Stock                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Expected term               2 years 10 months
Expected volatility rate               24.00%