Annual report pursuant to Section 13 and 15(d)

Equity Incentive Plans and Stock Based Compensation - Weighted-Average Fair Value Valuation Assumptions (Detail)

v3.8.0.1
Equity Incentive Plans and Stock Based Compensation - Weighted-Average Fair Value Valuation Assumptions (Detail) - Employee Stock Options - $ / shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Risk-free interest rate 2.06% 1.25%
Expected life (in years) 6 years 25 days 5 years
Dividend yield 0.00% 0.00%
Volatility 110.00% 76.00%
Weighted-average fair value of stock options granted $ 6.94 $ 1.31