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Stock-Based Compensation - VDI Units Granted (Details)
12 Months Ended
Dec. 31, 2020
$ / shares
shares
2019 VDI Plan  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
VDI units granted (in shares) | shares 385,455
Weighted-average grant date fair value (in dollars per share) | $ / shares $ 9.05
2018 VDI Plan  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
VDI units granted (in shares) | shares 116,844
Weighted-average grant date fair value (in dollars per share) | $ / shares $ 9.77
2017 VDI Plan  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
VDI units granted (in shares) | shares 68,866
Weighted-average grant date fair value (in dollars per share) | $ / shares $ 10.75