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Share-Based Compensation - Summary of Activity Related to Stock Options Granted under Company's Incentive Plan (Detail)
$ / shares in Units, $ in Thousands
9 Months Ended
Sep. 30, 2018
USD ($)
$ / shares
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Total Shares outstanding, Beginning balance 694,000
Total Shares, Granted 0
Total Shares, Exercised (130,000)
Total Shares, Forfeited, canceled or expired 0
Total Shares outstanding, Ending balance 564,000
Total Shares, Exercisable 564,000
Employee Stock Option [Member]  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Total Shares, Granted 0
Weighted Average Exercise Price per Share Outstanding, Beginning balance | $ / shares $ 17.31
Weighted Average Exercise Price per Share, Granted | $ / shares 0
Weighted Average Exercise Price per Share, Exercised | $ / shares 16.07
Weighted Average Exercise Price per Share, Forfeited, canceled or expired | $ / shares 0
Weighted Average Exercise Price per Share Outstanding, Ending balance | $ / shares 17.60
Weighted Average Exercise Price per Share, Exercisable | $ / shares $ 17.60
Weighted Average Remaining Contractual Term (Years), Outstanding 2 years 10 days
Weighted Average Remaining Contractual Term (Years), Exercisable 2 years 10 days
Aggregate Intrinsic Value, Outstanding | $ $ 53,657
Aggregate Intrinsic Value, Exercisable | $ $ 53,657