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Stock Options and Other Equity-Based Incentive Instruments - Summary of Options Outstanding (Detail) - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]      
Number of options (in shares) 128,500 160,500 343,000
Weighted average exercise price (in USD per share) $ 17.72 $ 17.60 $ 16.67
Intrinsic value (in thousands) $ 2,277    
Weighted average remaining contractual term (yrs.) 1 year 11 months 23 days    
Currently Exercisable      
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]      
Number of options (in shares) 128,500    
Weighted average exercise price (in USD per share) $ 17.72    
Intrinsic value (in thousands) $ 2,277    
Weighted average remaining contractual term (yrs.) 1 year 11 months 23 days    
Currently Not Exercisable      
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]      
Number of options (in shares) 0    
Weighted average exercise price (in USD per share) $ 0    
Intrinsic value (in thousands) $ 0    
Weighted average remaining contractual term (yrs.) 0 years