Stock-Based Compensation - Summary of Stock-based Compensation Expense Recognized (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense included in expenses	$ 341,258	$ 490,245	$ 743,497	$ 1,114,799
Research and development expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense included in expenses	100,579	176,609	217,358	368,769
General and administrative expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense included in expenses	240,679	313,636	526,139	746,030
Stock options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense included in expenses	150,246	237,285	374,957	607,858
Restricted stock and restricted stock units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense included in expenses	178,119	243,036	341,242	486,029
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense included in expenses	$ 12,893	$ 9,924	$ 27,298	$ 20,912