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Share-Based Compensation - 2012 Equity Incentive Plan (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2012
Stock options    
Class of Stock [Line Items]    
Vesting period 4 years  
Total unrecognized compensation cost $ 0.6  
Weighted-average period of unvested cost 1 year 2 months 12 days  
Restricted stock units    
Class of Stock [Line Items]    
Vesting period 4 years  
Total unrecognized compensation cost $ 9.3  
Weighted-average period of unvested cost 2 years 6 months  
Restricted stock units | Non-Management Trustees    
Class of Stock [Line Items]    
Vesting period 1 year  
2012 Equity Incentive Plan | Stock options    
Class of Stock [Line Items]    
Expiration period 10 years  
2012 Equity Incentive Plan | Class A common shares/units    
Class of Stock [Line Items]    
Shares available for issuance (in shares)   6,000,000