Net loss per share attributable to common stockholders - Schedule of antidilutive securities excluded from computation of earnings per share (Detail) - shares	6 Months Ended
	Jul. 31, 2020	Jul. 31, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	6,260,263	6,952,444
Stock options to purchase common stock and restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	6,185,126	6,649,129
Warrants to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	75,137	303,315