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Share-Based Compensation - Restricted Stock Unit Awards - Narrative (Details) - Restricted Stock Unit Awards - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2021
Sep. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Recognized share-based compensation expense (benefit) $ 0.9 $ 1.1 $ 2.7 $ 3.2
Unrecognized compensation cost, net of estimated forfeitures $ 6.8   $ 6.8  
Weighted-average period over which unrecognized compensation cost is expected to be recognized (years)     2 years 7 months 6 days