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Benefit Plans - Shares Granted to Certain Employees and Trustees (Details) - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2018
Dec. 31, 2017
Performance Shares        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Number of shares granted (in shares)     662,044 452,737
Measurement period (in years) 3 years      
Number of shares vested (in shares) 662,044 122,779    
Index Performance Shares        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Number of shares granted (in shares) 297,636 232,993    
Value per share granted (usd per share) $ 7.13 $ 6.59    
Peer Performance Shares        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Number of shares granted (in shares) 297,632 232,987    
Value per share granted (usd per share) $ 6.23 $ 5.97    
Non-vested Common Shares        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Number of shares granted (in shares) 304,060 243,270    
Grant date fair value $ 3,080 $ 2,581    
Vesting period (in years) 3 years