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Equity - 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
shares
Dec. 31, 2015
USD ($)
$ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Expected volatility rate look-back period         6 years    
Period of service, upon completion of which, grantee's LTIP unit and restricted stock awards will immediately vest         10 years    
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]              
Unvested beginning balance, per share (USD per share) | $ / shares         $ 10.01    
Vested, weighted average grant price, per share (USD per share) | $ / shares         11.97    
Granted, weighted average grant price, per share (USD per share) | $ / shares         13.77    
Forfeited or unearned, weighted average grant price, per share (USD per share) | $ / shares         5.36    
Unvested ending balance, per share (USD per share) | $ / shares         $ 11.20 $ 10.01  
Age of grantee at which LTIP unit and restricted stock awards immediately vest         60 years    
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 | $         $ 19.4 $ 18.4 $ 6.6
Expected term         2 years 9 months 18 days    
Risk-free interest rate         1.55%    
Expected price volatility         20.00%    
Share-based compensation arrangement by share-based payment award, fair value assumptions, expected dividend rate         2.05% 2.10% 1.90%
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]              
Granted, weighted average grant price, per share (USD per share) | $ / shares         $ 13.77 $ 9.60 $ 13.36
Long-Term Incentive Plan Unit and Restricted Stock [Member] | Maximum [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Expected term             3 years
Risk-free interest rate             1.00%
Expected price volatility             29.00%
Long-Term Incentive Plan Unit and Restricted Stock [Member] | Minimum [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Expected term           2 years 9 months 12 days 2 years 10 months 24 days
Risk-free interest rate           0.84% 0.80%
Expected price volatility           24.00% 24.00%
Time Based Long-Tern Incentive Plan Unit [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Fair value of share-based awards granted in period | $   $ 1.6   $ 1.4   $ 0.1  
Restricted Stock and LTIP Unit Activity [Roll Forward]              
Granted (in shares)   47,993   47,168      
Performance Based Long-Term Incentive Plan Unit [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Fair value of share-based awards granted in period | $   $ 1.0   $ 0.8      
Restricted Stock and LTIP Unit Activity [Roll Forward]              
Granted (in shares)   95,156   112,925      
Time Restricted Shares [Member]              
Restricted Stock and LTIP Unit Activity [Roll Forward]              
Granted (in shares)   34,407   44,198      
Restricted Stock [Member]              
Restricted Stock and LTIP Unit Activity [Roll Forward]              
Unvested beginning balance (in shares)         107,793    
Vested (in shares)         (48,900)    
Granted (in shares)         34,407    
Forfeited or unearned (in shares)         (2,509)    
Unvested ending balance (in shares)         90,791 107,793  
Long-Term Incentive Plan Unit [Member]              
Restricted Stock and LTIP Unit Activity [Roll Forward]              
Unvested beginning balance (in shares)         2,881,629    
Vested (in shares)         (588,367)    
Granted (in shares)         1,372,574    
Forfeited or unearned (in shares)         (77,227)    
Unvested ending balance (in shares)         3,588,609 2,881,629  
Long-Term Incentive Plan Units and Restricted Stock [Member]              
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]              
Fair value vested in period | $         $ 7.6 $ 5.1 $ 3.5
Awards that Meet Age and Service Requirements for Vesting [Member]              
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]              
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, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]              
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    
Director [Member] | 2013 Plan Units Granted In May 2017 [Member] | Time Based Long-Tern Incentive Plan Unit [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Fair value of share-based awards granted in period | $ $ 1.0            
Award vesting period 3 years            
Restricted Stock and LTIP Unit Activity [Roll Forward]              
Granted (in shares) 50,408            
Director [Member] | 2013 Plan Units Vesting June 2019 [Member] | Time Based Long-Tern Incentive Plan Unit [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Fair value of share-based awards granted in period | $     $ 0.8        
Award vesting period     3 years        
Restricted Stock and LTIP Unit Activity [Roll Forward]              
Granted (in shares)     43,257        
Executive Officer [Member] | 2013 Plan Units, Granted in March 2017 [Member] | Time Based Long-Tern Incentive Plan Unit [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Fair value of share-based awards granted in period | $   $ 6.1          
Award vesting period   4 years          
Number of vesting installments (vesting_installment) | vesting_installment   3          
Restricted Stock and LTIP Unit Activity [Roll Forward]              
Granted (in shares)   313,275          
Executive Officer [Member] | 2013 Plan Units, Granted in March 2017 [Member] | Performance Based Long-Term Incentive Plan Unit [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Fair value of share-based awards granted in period | $   $ 9.6          
Award vesting period   3 years          
Number of vesting installments (vesting_installment) | vesting_installment   2          
Restricted Stock and LTIP Unit Activity [Roll Forward]              
Granted (in shares)   865,742          
Executive Officer [Member] | 2013 Plan Units Vesting February 2020 [Member] | Time Based Long-Tern Incentive Plan Unit [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Fair value of share-based awards granted in period | $       $ 5.6      
Award vesting period       4 years      
Number of vesting installments (vesting_installment) | vesting_installment       3      
Restricted Stock and LTIP Unit Activity [Roll Forward]              
Granted (in shares)       368,225      
Executive Officer [Member] | 2013 Plan Units Vesting February 2020 [Member] | Performance Based Long-Term Incentive Plan Unit [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Fair value of share-based awards granted in period | $       $ 8.8      
Award vesting period       3 years      
Number of vesting installments (vesting_installment) | vesting_installment       2      
Restricted Stock and LTIP Unit Activity [Roll Forward]              
Granted (in shares)       1,230,228      
Executive Officer [Member] | 2013 Plan Units Vesting February 2021 [Member] | Time Based Long-Tern Incentive Plan Unit [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
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%      
Restricted Stock and LTIP Unit Activity [Roll Forward]              
Granted (in shares)       62,814      
2013 Plan [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Number of shares authorized under the plan (shares)         12,200,000    
Number of shares that remain available for future issuance (shares)         7,000,000