Condensed Statements of Comprehensive Loss - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (6,851,603)	$ (6,452,342)	$ (13,878,027)	$ (10,540,477)
Other comprehensive income, net of tax effect:
Unrealized gain on short and long-term investments	4,522		43,873
Comprehensive loss	(6,847,081)	(6,452,342)	(13,834,154)	(10,540,477)
Less: Accretion of stock issuance costs		(10,969)		(35,046)
Less: Accretion of Series E warrant discount		(40,146)		(127,616)
Less: Accretion of Series D and E redeemable convertible preferred stock dividends		(367,350)		(1,165,932)
Comprehensive loss attributable to common stockholders	$ (6,847,081)	$ (6,870,807)	$ (13,834,154)	$ (11,869,071)