Net Loss per Share - Outstanding Securities Excluded from Computation of Diluted Net Loss per Share (Detail) - shares	6 Months Ended
	Jun. 30, 2018	Jun. 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	1,693,575	1,436,978
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	26,666	208,999
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	766,381