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Share Based Compensation - Summarized Activity of Cash-Settled Stock Appreciation Rights (Detail) - Stock Appreciation Rights (SARs) - 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, Non-Option Equity Instruments, Outstanding [Roll Forward]    
Balance at beginning of year 374  
Granted, rights outstanding 0  
Exercised, rights outstanding (234)  
Forfeited, rights outstanding (140)  
Balance at end of period 0 374
Exercisable at end of period, rights outstanding 0  
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]    
Non-vested at beginning of year, weighted average grant date fair value $ 12.97  
Granted, weighted average exercise price 0.00  
Exercised, weighted average exercise price 10.14  
Forfeited, weighted average grant date 17.69  
Non-vested at end of period, weighted average grant date fair value 0.00 $ 12.97
Exercisable at end of period, weighted average exercise price $ 0.00  
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]    
Exercisable at end of period, weighted average remaining contractual terms 0 years 3 years
Weighted average remaining contractual term 0 years  
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value [Abstract]    
Aggregate intrinsic value $ 0 $ 773
Exercisable at end of period, aggregate intrinsic value $ 0