Net Loss per Share - Outstanding Securities Excluded from Computation of Diluted Net Loss per Share (Detail) - shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 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	1,486,559	1,441,924
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	16,666	256,499
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	755,178