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Share-Based Compensation - Summary of Option Activity Under 2013 Plan (Detail) - Option Activity Under the 2013 Plan [Member]
$ / shares in Units, $ in Thousands
 12 Months Ended
Dec. 31, 2017
USD ($)
$ / shares
shares
Schedule Of Stock Option Activity [Line Items]  
Option outstanding, Shares, Beginning balance | shares 286,586
Option granted, Shares | shares 43,502
Option Exercised, Shares | shares (108,434)
Option forfeited, Shares | shares (5,871)
Option outstanding, Shares, Ending balance | shares 215,783
Option Exercisable, Shares, Ending balance | shares 88,036
Option outstanding, Weighted Average Exercise Price, Beginning balance | $ / shares $ 15.08
Option Granted, Weighted Average Exercise Price | $ / shares 25.14
Option Exercised, Weighted Average Exercise Price | $ / shares 14.77
Option Forfeited, Weighted Average Exercise Price | $ / shares 15.64
Option Outstanding, Weighted Average Exercise Price, Ending balance | $ / shares 17.25
Option Exercisable, Weighted Average Exercise Price, Ending balance | $ / shares $ 14.77
Option Outstanding, Weighted Average Remaining Contractual Term 7 years 8 months 9 days
Option Exercisable, Weighted Average Remaining Contractual Term 6 years 7 months 13 days
Option outstanding, Aggregate Intrinsic Value | $ $ 2,276,823
Option Exercisable, Aggregate Intrinsic Value | $ $ 1,147,538