Condensed Statements of Comprehensive Loss - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (6,488,442)	$ (5,157,663)	$ (20,366,469)	$ (15,698,139)
Other comprehensive income (loss), net of tax effect:
Unrealized gain (loss) on short and long-term investments	(2,836)	12,993	41,037	4,754
Comprehensive loss	(6,491,278)	(5,144,670)	(20,325,432)	(15,693,385)
Less: Accretion of stock issuance costs				(35,046)
Less: Accretion of Series E warrant discount				(127,616)
Less: Accretion of Series D and E redeemable convertible preferred stock dividends				(1,165,932)
Comprehensive loss attributable to common stockholders	$ (6,491,278)	$ (5,144,670)	$ (20,325,432)	$ (17,021,979)