Quarterly report pursuant to Section 13 or 15(d)

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

v3.19.1
Stock Based Compensation - Summary of Stock-based Compensation Reflected within Statements of Operations (Detail) - USD ($)
3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]    
Share-based Compensation, Total $ 3,171,392 $ 4,609,208
Research and Development Expense [Member]    
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]    
Allocated share-based compensation expense 1,656,553 3,058,530
Selling and Marketing Expense [Member]    
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]    
Allocated share-based compensation expense 377,048 281,358
General and Administrative Expense [Member]    
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]    
Allocated share-based compensation expense $ 1,137,791 $ 1,269,320