Net Loss per Share - Reconciliation of Numerator and Denominator Used in Computing Basic and Diluted Net Loss per Share (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Numerator:
Net loss	$ (26,039,550)	$ (21,397,791)
Accretion of stock issuance costs	0	(35,046)
Accretion of Series E warrant discount		(127,616)
Accretion of Series D and E redeemable convertible preferred stock dividends		(1,165,932)
Net loss attributable to common stockholders	$ (26,039,550)	$ (22,726,385)
Denominator:
Weighted-average common shares outstanding-basic and diluted	7,113,075	4,518,499
Net loss per share attributable to common stockholders, basic and diluted	$ (3.66)	$ (5.03)
Series E Warrants
Numerator:
Accretion of Series E warrant discount	$ 0	$ (127,616)