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Stock-Based Compensation - Summary of Stock Option Activity (Detail) - 2014 Equity Incentive Plan [Member] - $ / shares
3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Number of Options, Outstanding, December 31, 2018 4,004,422  
Number of Options, Granted 957,000 596,000
Number of Options, Exercised (17,291)  
Number of Options, Forfeited (18,490)  
Number of Options, Outstanding, March 31, 2019 4,925,641  
Number of Options, Options exercisable, March 31, 2019 2,134,424  
Weighted-Average Exercise Price, Outstanding, December 31, 2018 $ 13.34  
Weighted-Average Exercise Price, Granted 16.06  
Weighted-Average Exercise Price, Exercised 13.52  
Weighted-Average Exercise Price, Forfeited 16.55  
Weighted-Average Exercise Price, Outstanding, March 31, 2019 $ 13.86