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Share Incentive and Other Compensation - Narrative (Details) - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2009
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Compensation expense $ 0.2 $ 0.2  
Trustee fees 1.2 1.1  
Total unrecognized compensation cost related to nonvested awards $ 14.3    
Weighted-average period over which cost is expected to be recognized 2 years 2 months    
LTIP Units      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Total fair value of shares that vested $ 7.3 13.6  
Restricted Stock      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Total fair value of shares that vested 0.7 0.7  
LTIP Units and Restricted Stock      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Total value of restricted shares and LTIP units as of the grant date 9.5    
Compensation expense 7.3 2.2  
Unit based compensation $ 8.4 $ 10.9  
Weighted average grant date fair value, grants (in dollars per share) $ 31.69 $ 34.34  
Officers and Employees | Second Amended 2016 Plan      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of shares authorized 1,756,317    
Officer | LTIP Units      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares issued during period, share-based compensation, net of forfeitures 306,635    
Officer | Restricted Stock      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares issued during period, share-based compensation, net of forfeitures 7,628    
Trustee | LTIP Units      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares issued during period, share-based compensation, net of forfeitures 11,105    
Trustee | LTIP Units | Tranche 1      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares issued during period, share-based compensation, net of forfeitures 5,805    
Trustee | LTIP Units | Tranche 2      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares issued during period, share-based compensation, net of forfeitures 5,300    
Senior Executives | Long Term Investment Alignment Program      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Max percentage of future fund III promote that may be awarded to senior executives     25.00%
General and Administrative Expense | LTIP Units and Restricted Stock      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Unit based compensation $ 8.4 $ 10.9  
Trustee | Restricted Stock      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares issued during period, share-based compensation, net of forfeitures 11,814    
Shares granted to trustees for trustee fees vesting on one year anniversary of grant date 3,864    
Shares granted to trustees for trustee fees begin vesting on two year anniversary of grant date 7,950    
Trustee | LTIP Units and Restricted Stock      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Award vesting period 3 years    
Annual vesting rate of shares granted to trustees that begin vesting on the second anniversary of grant date 33.00%    
Fund III | Long Term Investment Alignment Program      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Compensation expense $ 0.6 $ 5.0  
Fund III | Senior Executives | Long Term Investment Alignment Program      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Percentage of promote awarded as share based compensation award     25.00%
Fund IV | Senior Executives | Long Term Investment Alignment Program      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Percentage of promote awarded as share based compensation award     14.40%