Condensed Statements of Comprehensive Loss - USD ($)	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (7,026,424)	$ (4,088,134)
Other comprehensive income, net of tax effect:
Unrealized gain on short and long-term investments	39,351
Comprehensive loss	(6,987,073)	(4,088,134)
Less: Accretion of stock issuance costs		(24,077)
Less: Accretion of Series E warrant discount		(87,470)
Less: Accretion of Series D and E redeemable convertible preferred stock dividends		(798,582)
Comprehensive loss attributable to common stockholders	$ (6,987,073)	$ (4,998,263)