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Stock Options and Other Equity-Based Incentive Instruments - Summary of Options Outstanding (Detail) - USD ($)
$ / shares in Units, $ in Thousands
3 Months Ended
Mar. 31, 2018
Dec. 31, 2017
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]    
Number of options 446,400 446,400
Weighted average exercise price $ 16.84 $ 16.84
Intrinsic value (in thousands) $ 9,096  
Weighted average remaining contractual term (yrs.) 3 years 8 months 12 days  
Currently Exercisable [Member]    
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]    
Number of options 423,600  
Weighted average exercise price $ 16.65  
Intrinsic value (in thousands) $ 8,713  
Weighted average remaining contractual term (yrs.) 3 years 7 months 6 days  
Currently Not Exercisable [Member]    
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]    
Number of options 22,800  
Weighted average exercise price $ 20.45  
Intrinsic value (in thousands) $ 382  
Weighted average remaining contractual term (yrs.) 5 years 6 months