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 9 Months Ended 12 Months Ended
Sep. 30, 2018
Jun. 30, 2018
Sep. 30, 2018
Sep. 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    
Number of shares, Stock options exercised (shares) 0   (25,750) (22,125)  
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) $ 17.52   $ 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) 17.52 $ 17.52 17.52   $ 17.86
Weighted-Average Exercise Price Per Share, Options exercisable at end of period (in usd per share) $ 17.52   $ 17.52    
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 1 month 24 days 5 years 5 months 24 days 5 years 1 month 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 1 month 24 days 5 years 5 months 24 days 5 years 1 month 24 days   5 years 10 months 24 days
Weighted-Average Remaining Contractual Life, Options exercisable at end of period 5 years 1 month 24 days   5 years 1 month 24 days    
Aggregate Intrinsic Value of In-the-Money Options, Options outstanding at beginning of period $ 3,657   $ 4,548    
Aggregate Intrinsic Value of In-the-Money Options, Options outstanding at end of period 2,498 $ 3,657 2,498   $ 4,548
Aggregate Intrinsic Value of In-the-Money Options, Options exercisable at end of period $ 2,498   $ 2,498    
Intrinsic value represents the excess of the closing stock price related to options outstanding (in usd per share) $ 24.90 $ 28.35 $ 24.90   $ 30.35