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Share-Based Compensation (Detail) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of shares received per restricted stock unit (in shares) 1    
Total compensation cost related to nonvested awards, unrecognized $ 24,201   $ 32,812
Weighted-average period to recognize compensation cost (in years) 2 years    
Aggregate intrinsic value for outstanding SARs and RSUs $ 64,069    
Aggregate intrinsic value for vested SARs and RSUs $ 32,688    
Weighted-average remaining contractual life for outstanding SARs and RSUs (in years) 6 years    
Weighted-average remaining contractual life for exercisable SARs and RSUs, (in years) 5 years    
Share-based compensation $ 3,686 $ 2,717  
Outstanding options to purchase common shares not included in dilutive shares (in shares) 1,334,000 1,279,000  
Minimum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based payment award granted vesting period range (in years) 1 year    
Share-based payment, awards exercise period (in years and months) 12 months    
Maximum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based payment award granted vesting period range (in years) 5 years    
Share-based payment, awards exercise period (in years and months) 10 years