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Share-Based Compensation - Performance Restricted Stock Units - Narrative (Details) - PRSUs
shares in Thousands, $ in Millions
3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2020
USD ($)
shares
Sep. 30, 2019
USD ($)
shares
Sep. 30, 2020
USD ($)
metric
shares
Sep. 30, 2019
USD ($)
shares
Dec. 31, 2019
metric
shares
Dec. 31, 2018
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Number of performance award metrics     4      
Number of additional performance award metrics     2      
Number of units increased (decreased) during the period (in shares) | shares     (146) (33) 1 (3)
Recognized share-based compensation expense (benefit) | $ $ 0.2 $ 0.5 $ 0.8 $ 1.2    
Unrecognized compensation cost | $ $ 1.3   $ 1.3      
Nonvested shares outstanding (in shares) | shares 329 354 329 354 260 277
Weighted-average period over which unrecognized compensation cost is expected to be recognized (years)     1 year 9 months 18 days      
Executive and Senior Officers            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Performance period (years)     1 year      
Number of performance award metrics         3  
Requisite service period (years)     5 years      
Executive and Senior Officers | Anniversary 1            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Award vesting rights, percentage     25.00%      
Executive and Senior Officers | Anniversary 2            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Award vesting rights, percentage     25.00%      
Executive and Senior Officers | Anniversary 3            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Award vesting rights, percentage     25.00%      
Executive and Senior Officers | Anniversary 4            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Award vesting rights, percentage     25.00%