Preferred Stock, Common Stock and Stockholders' Equity - Summary of Recognized Non-Cash Stock-Based Compensation Expense (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 1,102,087	$ 145,966
Research and development [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	410,150	39,638
General and administrative [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 691,937	$ 106,328