Quarterly report pursuant to Section 13 or 15(d)

Stock Based Compensation - Summary of Fair Values of Stock Options Granted (Detail)

v3.19.3
Stock Based Compensation - Summary of Fair Values of Stock Options Granted (Detail) - Employee Stock Purchase Plan [Member] - Employee Stock Option [Member] - $ / shares
9 Months Ended
Sep. 30, 2019
Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Dividend yield 0.00% 0.00%
Expected volatility, minimum 83.00% 72.00%
Expected volatility, maximum 96.00% 177.00%
Risk-free interest rate, minimum 2.10% 1.61%
Risk-free interest rate, maximum 2.51% 2.14%
Expected life 6 months 6 months
Minimum [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Stock price $ 4.27 $ 14.48
Maximum [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Stock price $ 5.79 $ 22.34