Quarterly report pursuant to Section 13 or 15(d)

Stock Based Compensation - Weighted-Average Fair Value Valuation Assumptions (Detail)

v3.10.0.1
Stock Based Compensation - Weighted-Average Fair Value Valuation Assumptions (Detail) - Employee Stock Options - $ / shares
3 Months Ended 9 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Risk-free interest rate 3.01% 1.85% 2.79% 1.85%
Expected term (in years) 6 years 25 days 6 years 1 month 2 days 6 years 10 days 6 years 18 days
Dividend yield 0.00% 0.00% 0.00% 0.00%
Volatility 109.00% 113.00% 107.00% 111.00%
Weighted-average fair value of stock options granted $ 4.50 $ 5.57 $ 5.82 $ 5.40