Net Loss per Share - Reconciliation of Numerator and Denominator Used in Computing Basic and Diluted Net Loss per Share (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Numerator:
Net loss	$ (7,026,424)	$ (4,088,134)
Accretion of stock issuance costs		(24,077)
Accretion of Series E warrant discount		(87,470)
Series E and D, Convertible Preferred Stock dividends		(798,582)
Net loss attributable to common stockholders	$ (7,026,424)	$ (4,998,263)
Denominator:
Weighted-average common shares outstanding-basic and diluted	6,885,522	333,408
Net loss per share attributable to common stockholders, basic and diluted	$ (1.02)	$ (14.99)
Series E Warrants
Numerator:
Accretion of Series E warrant discount		$ (87,470)