Annual report pursuant to Section 13 and 15(d)

Share-based Compensation - Summary of Stock Option Transactions under Plans (Detail)

v3.20.4
Share-based Compensation - Summary of Stock Option Transactions under Plans (Detail) - 2007 and 2013 Plan - $ / shares
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]      
Number of Shares, options outstanding at beginning of period (shares) 156,438 338,338 364,088
Number of Shares, Options exercised (shares)   (181,900) (25,750)
Number of Shares, Options forfeited (shares) (30,500)    
Number of Shares, Options outstanding at end of period (shares) 125,938 156,438 338,338
Number of Shares, Options exercisable at end of period (shares) 125,938 156,438 338,338
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]      
Weighted-Average Exercise Price Per Share, Options outstanding at beginning of period (in USD per share) $ 18.84 $ 17.52 $ 17.86
Weighted-Average Exercise Price Per Share, Options exercised (in USD per share)   16.38 22.06
Weighted-Average Exercise Price Per Share, Options forfeited (in USD per share) 15.73    
Weighted-Average Exercise Price Per Share, Options outstanding at end of period (in USD per share) 19.59 18.84 17.52
Weighted-Average Exercise Price Per Share, Options exercisable at end of period (in USD per share) $ 19.59 $ 18.84 $ 17.52