Statements of Comprehensive Loss - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (21,397,791)	$ (13,958,408)
Other comprehensive loss, net of tax effect:
Unrealized loss on short and long-term investments	(41,357)
Comprehensive loss	(21,439,148)	(13,958,408)
Accretion of stock issuance costs	(35,046)	(102,677)
Accretion of Series E warrant discount	(127,616)	(313,152)
Accretion of Series D and E redeemable convertible preferred stock dividends	(1,165,932)	(3,244,572)
Comprehensive loss attributable to common stockholders	$ (22,767,742)	$ (17,618,809)