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Share-based Compensation - Summary of RSU Activity (Detail) - Restricted Stock Units (RSUs) [Member] - $ / shares
shares in Thousands
3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Non-vested units at January 1, 2019 182  
Granted (target) 39  
Achieved performance adjustment 8  
Vested (54)  
Forfeited 0  
Non-vested units at March 31, 2019 175  
Weighted Average Grant Date Fair Value, Non-vested units at January 1, 2019 $ 21.89  
Weighted Average Grant Date Fair Value, Granted (target) 27.89 $ 28.25
Weighted Average Grant Date Fair Value, Achieved performance adjustment 16.98  
Weighted Average Grant Date Fair Value, Vested 16.98  
Weighted Average Grant Date Fair Value, Forfeited 0  
Weighted Average Grant Date Fair Value Non-vested units at March 31, 2019 $ 24.55