Net Loss per Share - Calculation of Basic and Diluted Net Loss per Share (Details) (USD $)	3 Months Ended			9 Months Ended
	Sep. 30, 2014	Mar. 25, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Numerator:
Net loss	$ (9,348,391)		$ (3,767,890)	$ (26,663,829)	$ (7,219,236)
Accretion on preferred stock		(86,899,555)	(2,748,232)	(86,899,555)	(52,861,367)
Net loss applicable to common stockholders	$ (9,348,391)		$ (6,516,122)	$ (113,563,384)	$ (60,080,603)
Denominator:
Weighted-average number of common shares – basic and diluted	19,691,167		546,714	13,920,651	509,425
Net loss per share applicable to common stockholders—basic and diluted	$ (0.47)		$ (11.92)	$ (8.16)	$ (117.94)