Stock-Based Compensation - Summary of Recognized Compensation Cost Related to Employee and Non-employee Stock-Based Compensation Activity (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]
Stock-based compensation expense	$ 604,661	$ 877,757	$ 1,226,346	$ 1,957,478
Research and development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	73,463	114,949	232,794	174,013
General and administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 531,198	$ 762,808	$ 993,552	$ 1,783,465