Net Loss per Share - Outstanding Securities Excluded from Computation of Diluted Net Loss per Share (Detail) - shares	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Options to purchase common stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	2,148,323	1,532,979
Restricted Stock Units R S U
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	249,166	34,999
Warrant | Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	237,846	219,723
QNAH convertible note
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	772,075