Stock-Based Compensation - Compensation Cost Related to Share-Based Awards (Details) (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]
Stock based compensation expense	$ 1,234,756	$ 330,259	$ 5,123,564	$ 438,052
Research and development
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock based compensation expense	582,900	24,222	2,489,049	63,684
General and administrative
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock based compensation expense	$ 651,856	$ 306,037	$ 2,634,515	$ 374,368