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Share-Based Employee Compensation - Summary of Total Number of SARs Granted (Detail) - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Schedule of Share based Compensation Arrangements by Share based Payment Award, Performance Options [Line Items]      
Allocated Share-based Compensation Expense $ 12,615 $ 9,285 $ 11,220
Stock Appreciation Rights (SARs)      
Schedule of Share based Compensation Arrangements by Share based Payment Award, Performance Options [Line Items]      
Allocated Share-based Compensation Expense $ (32) $ 320 $ 3,288
Number of Share units      
Nonvested number of Units, beginning balance 50    
Granted, number of units 0    
Exercised, number of units (50)    
Forfeited, number of units 0    
Vested, number of units, ending balance 0    
Weighted Average Grant Date Fair Value      
Nonvested weighted Average Grant Date Fair Value, beginning balance (in dollars per unit) $ 6.48    
Granted, weighted average grant date fair value (in dollars per unit) 0.00    
Exercised, weighted average exercise price (in dollars per unit) 6.48    
Forfeited, weighted average grant date fair value (in dollars per unit) 0.00    
Vested, Weighted Average Grant Date Fair Value, ending balance (in dollars per unit) $ 0.00