Quarterly report pursuant to Section 13 or 15(d)

Stock Based Compensation - Stock Option Activity Under Equity Incentive Plan (Detail)

v3.19.2
Stock Based Compensation - Stock Option Activity Under Equity Incentive Plan (Detail) - USD ($)
$ / shares in Units, $ in Millions
6 Months Ended 12 Months Ended
Jun. 30, 2019
Dec. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]    
Number of Shares, Outstanding, Beginning Balance 4,002,999  
Number of Shares, Granted 1,541,300  
Number of Shares, Exercised (146,151)  
Number of Shares, Forfeitures (292,335)  
Number of Shares, Outstanding, Ending Balance 5,105,813 4,002,999
Number of Shares, Exercisable 2,020,058  
Weighted-Average Exercise Price, Outstanding, Beginning Balance $ 10.43  
Weighted-Average Exercise Price, Granted 5.13  
Weighted-Average Exercise Price, Exercised 5.81  
Weighted-Average Exercise Price, Forfeitures 7.66  
Weighted-Average Exercise Price, Outstanding, Ending Balance 9.13 $ 10.43
Weighted-Average Exercise Price, Exercisable $ 13.43  
Weighted-Average Remaining Contractual Term, Outstanding 7 years 3 months 18 days 6 years 4 months 24 days
Weighted-Average Remaining Contractual Term, Exercisable 4 years 10 months 24 days  
Aggregate Intrinsic Value, Outstanding $ 12.0 $ 1.5
Aggregate Intrinsic Value, Exercisable $ 5.0