Net Loss Per Common Share (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Basic and diluted net loss per common share calculation:
Net loss and comprehensive loss	$ (10,615,483)	$ (15,534,872)	$ (35,063,979)	$ (36,403,967)
Accretion of redeemable convertible preferred stock				(28,521)
Net loss attributable to common stockholders	$ (10,615,483)	$ (15,534,872)	$ (35,063,979)	$ (36,432,488)
Weighted average common shares outstanding	44,214,428	26,366,300	41,443,362	23,036,366
Net loss per share of common stock-basic and diluted	$ (0.24)	$ (0.59)	$ (0.85)	$ (1.58)
Outstanding securities excluded from computation of diluted weighted shares outstanding as they would have been anti dilutive:
Outstanding securities excluded from computation of diluted weighted shares outstanding (in shares)			4,685,788	3,582,382
Stock options
Outstanding securities excluded from computation of diluted weighted shares outstanding as they would have been anti dilutive:
Outstanding securities excluded from computation of diluted weighted shares outstanding (in shares)			4,657,949	3,552,124
Warrants
Outstanding securities excluded from computation of diluted weighted shares outstanding as they would have been anti dilutive:
Outstanding securities excluded from computation of diluted weighted shares outstanding (in shares)			27,839	30,258