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Share-Based Compensation - Summary of Total Stock Based Compensation Expense (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]      
Total stock based compensation expense $ 9,085 $ 8,785 $ 4,740
Stock Options [Member]      
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]      
Total stock based compensation expense 1,585 1,256 761
Restricted Stock or Units Settled in Stock [Member]      
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]      
Total stock based compensation expense 3,366 1,960 2,532
Restricted Stock Units Settled in Cash [Member]      
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]      
Total stock based compensation expense $ 4,134 $ 5,569 $ 1,447