Quarterly report pursuant to Section 13 or 15(d)

Stock Based Compensation - Summary of Stock-based Compensation Reflected within Statements of Operations (Detail)

v3.19.2
Stock Based Compensation - Summary of Stock-based Compensation Reflected within Statements of Operations (Detail) - USD ($)
3 Months Ended 6 Months Ended
Jun. 30, 2019
Jun. 30, 2018
Jun. 30, 2019
Jun. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]        
Share-based Compensation, Total $ 2,797,933 $ 4,342,880 $ 5,969,325 $ 8,952,088
Research and Development Expense [Member]        
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]        
Allocated share-based compensation expense 1,361,225 2,483,693 3,017,778 5,542,223
Selling and Marketing Expense [Member]        
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]        
Allocated share-based compensation expense 343,945 388,533 720,993 669,891
General and Administrative Expense [Member]        
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]        
Allocated share-based compensation expense $ 1,092,763 $ 1,470,654 $ 2,230,554 $ 2,739,974