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Share Based Compensation - Summarized Activity of Stock Option Awards (Detail) - Stock Options - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]    
Balance at beginning of year, options outstanding 1,836  
Granted, options outstanding 0  
Exercised, options outstanding (768)  
Forfeited, options outstanding (1,068)  
Balance at end of period, options outstanding 0 1,836
Exercisable at end of period, options outstanding 0  
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]    
Balance at beginning of year, weighted average exercise price $ 19.39  
Granted, weighted average exercise price 0.00  
Exercised, weighted average exercise price 14.07  
Forfeited, weighted average exercise price 23.21  
Balance at end of period, weighted average exercise price 0.00 $ 19.39
Exercisable at end of period, weighted average exercise price $ 0.00  
Share-based Compensation Arrangement by Share-based Payment Award, Options, Aggregate Intrinsic Value [Abstract]    
Weighted average remaining contractual term 0 years 5 years
Exercisable at end of period, weighted average remaining contractual term 0 years  
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]    
Aggregate intrinsic value $ 0 $ 449
Exercisable at end of period, aggregate intrinsic value $ 0