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Share-based Compensation - Summary of Additional RSU Information (Detail) - Restricted Stock Units (RSUs) [Member] - USD ($)
$ / shares in Units, $ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2019
Jun. 30, 2018
Jun. 30, 2019
Jun. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Weighted-average grant date fair value per unit $ 27.89 $ 28.25
Fair value of RSUs that vested $ 0 $ 0 $ 916 $ 0