Net loss per common stock - Schedule of Antidilutive Securities Excluded from Computation of Basic and Diluted Net Loss Per Common Stock (Detail) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from the computation of basic and diluted net loss per share	2,056,767	1,262,477	2,056,767	1,262,477
Outstanding Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from the computation of basic and diluted net loss per share	2,056,767	1,251,114	2,056,767	1,251,114
Warrants to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from the computation of basic and diluted net loss per share		11,363		11,363