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Share-Based Compensation (Details) - USD ($)
12 Months Ended
Jan. 17, 2020
Feb. 15, 2019
Jan. 18, 2019
Mar. 01, 2018
Feb. 16, 2018
Jan. 19, 2018
Mar. 01, 2017
Feb. 19, 2016
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                      
Compensation expense                 $ 3,000,000.0 $ 1,100,000 $ 1,000,000.0
Cash payments distributed related to awards previously granted and now payable                 1,500,000    
Awards forfeited during period, value                 $ 0 $ 0 $ 0
Awards forfeited during period, units                 0 0 0
Outstanding awards vested during period                 $ 6,200,000    
Performance Unit Plan [Member] | Performance Units [Member]                      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                      
Award vesting period                 5 years    
Awards granted (in units)   17,022     17,830   14,704 19,055      
Director Incentive Agreement [Member] | Performance Units [Member]                      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                      
Award vesting period                 3 years    
Awards granted (in units)     5,175 1,106   4,704          
Director Incentive Agreement [Member] | Performance Units [Member] | Subsequent Event [Member]                      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                      
Awards granted (in units) 5,048