Annual report pursuant to Section 13 and 15(d)

Share-based Compensation - Summary of Stock Options Outstanding under Plans (Detail)

v3.20.4
Share-based Compensation - Summary of Stock Options Outstanding under Plans (Detail) - $ / shares
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
2007 and 2013 Plan        
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]        
Options Outstanding, Number of Shares (shares) 125,938 156,438 338,338 364,088
Options Outstanding, Weighted-Average Exercise Price Per Share (in USD per share) $ 19.59 $ 18.84 $ 17.52 $ 17.86
Options Exercisable, Number of Shares (shares) 125,938 156,438 338,338  
Options Exercisable, Weighted-Average Exercise Price Per Share (in USD per share) $ 19.59 $ 18.84 $ 17.52  
Intrinsic value of stock options outstanding (in USD per share) 11.34      
$10.80 to $14.99        
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]        
Exercise Price Range, Lower Limit (in USD per share) 10.80      
Exercise Price Range, Upper Limit (in USD per share) $ 14.99      
$10.80 to $14.99 | 2007 and 2013 Plan        
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]        
Options Outstanding, Number of Shares (shares) 4,938      
Options Outstanding, Weighted-Average Exercise Price Per Share (in USD per share) $ 12.54      
Options Outstanding, Weighted-Average Remaining Contractual Life 1 year 11 months 12 days      
Options Exercisable, Number of Shares (shares) 4,938      
Options Exercisable, Weighted-Average Exercise Price Per Share (in USD per share) $ 12.54      
Options Exercisable, Weighted-Average Remaining Contractual Life 1 year 11 months 12 days      
$15.00 to $19.99        
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]        
Exercise Price Range, Lower Limit (in USD per share) $ 15.00      
Exercise Price Range, Upper Limit (in USD per share) $ 19.99      
$15.00 to $19.99 | 2007 and 2013 Plan        
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]        
Options Outstanding, Number of Shares (shares) 50,000      
Options Outstanding, Weighted-Average Exercise Price Per Share (in USD per share) $ 16.43      
Options Outstanding, Weighted-Average Remaining Contractual Life 2 years 7 months 28 days      
Options Exercisable, Number of Shares (shares) 50,000      
Options Exercisable, Weighted-Average Exercise Price Per Share (in USD per share) $ 16.43      
Options Exercisable, Weighted-Average Remaining Contractual Life 2 years 7 months 28 days      
$20.00 to $24.83        
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]        
Exercise Price Range, Lower Limit (in USD per share) $ 20.00      
Exercise Price Range, Upper Limit (in USD per share) $ 24.83      
$20.00 to $24.83 | 2007 and 2013 Plan        
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]        
Options Outstanding, Number of Shares (shares) 71,000      
Options Outstanding, Weighted-Average Exercise Price Per Share (in USD per share) $ 22.31      
Options Outstanding, Weighted-Average Remaining Contractual Life 3 years 10 months 2 days      
Options Exercisable, Number of Shares (shares) 71,000      
Options Exercisable, Weighted-Average Exercise Price Per Share (in USD per share) $ 22.31      
Options Exercisable, Weighted-Average Remaining Contractual Life 3 years 10 months 2 days