Quarterly report pursuant to Section 13 or 15(d)

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

v3.8.0.1
Stock Based Compensation - Weighted-Average Fair Value Valuation Assumptions (Detail) - Employee Stock Options - $ / shares
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Risk-free interest rate 2.68% 1.95%
Expected term (in years) 6 years 7 days 5 years
Dividend yield 0.00% 0.00%
Volatility 108.00% 76.00%
Weighted-average fair value of stock options granted $ 8.85 $ 0.82