Net Loss Per Share - Schedule of Anti-dilutive Weighted-Average Equity Instruments Excluded from Calculation of Diluted Net Loss Per Share (Detail) - shares	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share Basic [Line Items]
Anti-dilutive securities excluded from calculation of diluted net loss per share	4,472,887	3,629,158
Awards under Equity Incentive Plan [Member]
Earnings Per Share Basic [Line Items]
Anti-dilutive securities excluded from calculation of diluted net loss per share	2,634,295	1,607,078
Unvested Restricted Shares and Restricted Stock Units [Member]
Earnings Per Share Basic [Line Items]
Anti-dilutive securities excluded from calculation of diluted net loss per share	173,422	78,396
Derivative Call Option [Member]
Earnings Per Share Basic [Line Items]
Anti-dilutive securities excluded from calculation of diluted net loss per share		650,000
Warrants to Purchase Common Stock [Member]
Earnings Per Share Basic [Line Items]
Anti-dilutive securities excluded from calculation of diluted net loss per share	1,665,170	1,293,684