Annual report pursuant to Section 13 and 15(d)

Equity Incentive Plans and Stock Based Compensation - Summary of Stock Option Activity Under Equity Incentive Plan (Detail)

v3.19.1
Equity Incentive Plans and Stock Based Compensation - Summary of Stock Option Activity Under Equity Incentive Plan (Detail) - USD ($)
$ / shares in Units, $ in Millions
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]      
Outstanding Options Number of Shares, Beginning Balance 2,768,711 941,684  
Number of Shares, Options assumed in merger   963,681  
Number of Shares, Options granted 1,844,787 1,116,627  
Number of Shares, Options exercised (407,682) (17,473)  
Number of shares, Options canceled (202,817) (235,808)  
Outstanding Options Number of Shares, Ending Balance 4,002,999 2,768,711 941,684
Outstanding Options Number of Shares, Vested and expected to vest 4,002,999    
Outstanding Options Number of Shares, Exercisable 1,607,856    
Weighted Average Exercise Price, Beginning Balance $ 12.07 $ 0.92  
Weighted Average Exercise Price, Options assumed in merger   33.62  
Weighted Average Exercise Price, Options granted 6.98 8.30  
Weighted Average Exercise Price, Options exercised 0.70 3.66  
Weighted Average Exercise Price, Options canceled 20.83 35.48  
Weighted Average Exercise Price, Ending Balance 10.43 $ 12.07 $ 0.92
Weighted Average Exercise Price, Vested and expected to vest 10.43    
Weighted Average Exercise Price, Exercisable $ 15.19    
Weighted-Average Remaining Contractual Term, Outstanding 6 years 4 months 24 days 5 years 7 months 6 days 5 years 8 months 12 days
Weighted-Average Remaining Contractual Term, Vested and expected to vest 6 years 4 months 24 days    
Weighted-Average Remaining Contractual Term, Exercisable 3 years 8 months 12 days    
Aggregate Intrinsic Value, Outstanding $ 1.5 $ 11.0 $ 0.9
Aggregate Intrinsic Value, Vested and expected to vest 1.5    
Aggregate Intrinsic Value, Exercisable $ 1.5