Stockholders' Equity - Summary of Recognized Non-Cash Stock-Based Compensation Expense (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 452,236	$ 371,675	$ 1,298,279	$ 1,127,813
Research and development [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	177,767	144,719	487,704	433,252
General and administrative [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 274,469	$ 226,956	$ 810,575	$ 694,561