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Stock-Based Compensation - Summary of Stock-Based Compensation Expenses (Detail) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Stock-based compensation expense $ 2,306 $ 1,965
Stock Appreciation Rights [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Stock-based compensation expense 202 167
Time-Based Restricted Stock and Restricted Stock Units [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Stock-based compensation expense 822 737
Performance-Based Restricted Stock and Restricted Stock Units [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Stock-based compensation expense 1,249 1,039
Employee Stock Purchase Plan [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Stock-based compensation expense $ 33 $ 22