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)

v3.8.0.1
Equity Incentive Plans and Stock Based Compensation - Summary of Stock Option Activity Under Equity Incentive Plan (Detail) - USD ($)
$ / shares in Units, $ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]      
Outstanding Options Number of Shares, Beginning Balance 941,684 922,628  
Number of Shares, Options assumed in merger 963,681    
Number of Shares, Options granted 1,116,627 31,845  
Number of Shares, Options exercised (17,473) (1,513)  
Number of shares, Options canceled (235,808) (11,276)  
Outstanding Options Number of Shares, Ending Balance 2,768,711 941,684 922,628
Outstanding Options Number of Shares, Vested and expected to vest 2,768,711    
Outstanding Options Number of Shares, Exercisable 1,634,268    
Weighted Average Exercise Price, Beginning Balance $ 0.92 $ 0.89  
Weighted Average Exercise Price, Options assumed in merger 33.62    
Weighted Average Exercise Price, Options granted 8.30 1.85  
Weighted Average Exercise Price, Options exercised 3.66 1.64  
Weighted Average Exercise Price, Options canceled 35.48 1.10  
Weighted Average Exercise Price, Ending Balance 12.07 $ 0.92 $ 0.89
Weighted Average Exercise Price, Vested and expected to vest 12.07    
Weighted Average Exercise Price, Exercisable $ 14.76    
Weighted-Average Remaining Contractual Term, Outstanding 5 years 7 months 6 days 5 years 8 months 12 days 6 years 7 months 6 days
Weighted-Average Remaining Contractual Term, Vested and expected to vest 5 years 7 months 6 days    
Weighted-Average Remaining Contractual Term, Exercisable 2 years 9 months 18 days    
Aggregate Intrinsic Value, Outstanding $ 900 $ 900  
Aggregate Intrinsic Value, Outstanding 11,000 $ 900 $ 900
Aggregate Intrinsic Value, Vested and expected to vest 11,000    
Aggregate Intrinsic Value, Exercisable $ 8,900