Stockholders' Equity - Summary of Recognized Non-Cash Stock-Based Compensation Expense (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 418,912	$ 371,600
Research and development [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	158,788	143,024
General and administrative [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 260,124	$ 228,576