Quarterly report pursuant to Section 13 or 15(d)

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

v3.10.0.1
Stock Based Compensation - Stock Option Activity Under Equity Incentive Plan (Detail) - USD ($)
$ / shares in Units, $ in Millions
3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2017
Jun. 30, 2018
Dec. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]      
Number of Shares, Outstanding, Beginning Balance   2,768,711  
Stock options granted 0 1,772,037  
Number of Shares, Exercised   (166,868)  
Number of Shares, Forfeitures   (26,732)  
Number of Shares, Outstanding, Ending Balance   4,347,148 2,768,711
Number of Shares, Exercisable   1,496,349  
Weighted-Average Exercise Price, Outstanding, Beginning Balance   $ 12.07  
Weighted-Average Exercise Price, Granted   7.06  
Weighted-Average Exercise Price, Exercised   0.93  
Weighted-Average Exercise Price, Forfeitures   30.07  
Weighted-Average Exercise Price, Outstanding, Ending Balance   10.34 $ 12.07
Weighted-Average Exercise Price, Exercisable   $ 15.78  
Weighted-Average Remaining Contractual Term, Outstanding   7 years 3 months 18 days 5 years 7 months 6 days
Weighted-Average Remaining Contractual Term, Exercisable   2 years 9 months 18 days  
Aggregate Intrinsic Value, Outstanding   $ 3.2 $ 11.0
Aggregate Intrinsic Value, Exercisable   $ 3.2