Stockholders' Equity - Stockholders' Equity - Summary of Recognized Non-Cash Stock-Based Compensation Expense (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 303,961	$ 7,629	$ 792,481	$ 13,881
Research and development [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	105,145	313	302,569	4,377
General and administrative [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 198,816	$ 7,316	$ 489,912	$ 9,504