Organization, Liquidity and Management's Plan, and Summary of Significant Accounting Policies - Schedule of Computation of Basic and Diluted Net Loss per Common Share (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Numerator
Net loss attributable to common stockholders	$ (5,171,634)	$ (3,692,793)	$ (10,393,534)	$ (7,279,781)
Denominator
Weighted-average common shares outstanding	24,387,148	17,700,774	23,528,353	13,692,258
Less: Weighted-average shares subject to repurchase	(268,261)	(595,400)	(287,571)	(631,682)
Denominator for basic and diluted net loss per share	24,118,887	17,105,374	23,240,782	13,060,576
Basic and diluted net loss per share	$ (0.21)	$ (0.22)	$ (0.45)	$ (0.56)