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Share-Based Compensation - Additional Information (Detail) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2020
Sep. 30, 2019
Sep. 30, 2020
Sep. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Granted ( in shares) 0 100,000 0 100,000
Granted, Units fair value   $ 0.6   $ 0.6
Estimated pretax compensation expense $ 23.0   $ 23.0  
Expiration period in years     4 years  
Restricted Stock Units (RSUs)        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Granted ( in shares) 0 200,000 300,000 200,000
Granted, Units fair value   $ 4.4 $ 4.4 $ 4.4
Performance-based Restricted Stock Units [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Granted, Units fair value   $ 4.7 $ 3.9 $ 4.7
Granted ( in shares)   200,000 300,000 200,000
Service period in years     3 years