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Stock-based Compensation - Transactions Related to Grant of Restricted Stock Units to Employees and Directors (Detail) - Restricted Stock Units [Member]
3 Months Ended
Mar. 31, 2019
$ / shares
shares
Amount  
Unvested at December 31, 2018 | shares 554,147
Granted | shares 100,000
Vested | shares (35,599)
Unvested at March 31, 2019 | shares 618,548
Weighted average grant date fair value price  
Unvested at December 31, 2018 | $ / shares $ 9.34
Granted | $ / shares 11.53
Vested | $ / shares 8.00
Unvested at March 31, 2019 | $ / shares $ 9.77