Quarterly report pursuant to Section 13 or 15(d)

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

v3.10.0.1
Share-Based Compensation - Summary of Stock Options Outstanding under Plans (Detail) - USD ($)
$ / shares in Units, $ in Thousands
 3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2018
Mar. 31, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]            
Number of Shares, Options outstanding at beginning of period (shares) 338,338 364,088   364,088    
Number of shares, Stock options exercised (shares) 0   (10,500) (25,750) (11,500)  
Number of Shares, Options outstanding at end of period (shares) 338,338 338,338   338,338   364,088
Number of Shares, Options exercisable at end of period (shares) 338,338     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) $ 17.54 $ 17.86   $ 17.86    
Weighted-Average Exercise Price Per Share, Options exercised (in usd per share)       22.06    
Weighted-Average Exercise Price Per Share, Options outstanding at end of period (in usd per share) 17.54 $ 17.54   17.54   $ 17.86
Weighted-Average Exercise Price Per Share, Options exercisable at end of period (in usd per share) $ 17.54     $ 17.54    
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term [Abstract]            
Weighted-Average Remaining Contractual Life, Options outstanding at beginning of period 5 years 6 months 5 years 5 months 24 days   5 years 5 months 24 days   5 years 10 months 24 days
Weighted-Average Remaining Contractual Life, Options exercised       5 years 10 months 24 days    
Weighted-Average Remaining Contractual Life, Options outstanding at end of period 5 years 6 months 5 years 5 months 24 days   5 years 5 months 24 days   5 years 10 months 24 days
Weighted-Average Remaining Contractual Life, Options exercisable at end of period 5 years 5 months 24 days     5 years 5 months 24 days    
Aggregate Intrinsic Value of In-the-Money Options, Options outstanding at beginning of period $ 4,469 $ 4,548   $ 4,548    
Aggregate Intrinsic Value of In-the-Money Options, Options outstanding at end of period 3,657 $ 4,469   3,657   $ 4,548
Aggregate Intrinsic Value of In-the-Money Options, Options exercisable at end of period $ 3,657     $ 3,657    
Intrinsic value represents the excess of the closing stock price related to options outstanding (in usd per share) $ 28.35 $ 30.75   $ 28.35   $ 30.35