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Stock-Based Compensation - Fair Value of Restricted Stock Awards Vested (Detail) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2019
Jun. 30, 2018
Jun. 30, 2019
Jun. 30, 2018
Restricted Stock [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Fair value of restricted stock awards vested $ 3,992 $ 2,016 $ 5,232 $ 3,272