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Stock-Based Compensation - Summary of Stock Option Activity (Detail) - 2014 Equity Incentive Plan [Member] - $ / shares
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Number of Options, Outstanding at December 31, 2017 3,492,141  
Number of Options, Granted 596,000 748,500
Number of Options, Exercised (37,688)  
Number of Options, Forfeited (117,461)  
Number of Options, Outstanding at March 31, 2018 3,932,992  
Number of Options, Options exercisable at March 31, 2017 1,696,358  
Weighted-Average Exercise Price, Outstanding at December 31, 2017 $ 11.75  
Weighted-Average Exercise Price, Granted 14.09  
Weighted-Average Exercise Price, Exercised 6.97  
Weighted-Average Exercise Price, Forfeited 10.66  
Weighted-Average Exercise Price, Outstanding at March 31, 2018 $ 12.18