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Share-Based Payment Awards - Deferred Stock Units - Additional Information (Detail) - shares
1 Months Ended 9 Months Ended
Jan. 31, 2019
Sep. 30, 2021
Dec. 31, 2020
2016 Long Term Incentive Plan [Member]      
Class Of Stock [Line Items]      
Ratable annual vesting period of equity awards 4 years    
Non Executive Directors [Member]      
Class Of Stock [Line Items]      
Non-vested deferred stock units outstanding   0 0
Deferred Stock Units [Member]      
Class Of Stock [Line Items]      
Ratable annual vesting period of equity awards   1 year  
Deferred Stock Units [Member] | 2016 Long Term Incentive Plan [Member]      
Class Of Stock [Line Items]      
Vested deferred stock units vested   0