Earnings (loss) per share - Schedule of basic and diluted net loss per common stock (Detail) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Securities excluded from computation of earnings per share	6,972,441	16,468,693	6,972,441	16,468,693
Outstanding stock options [Member]
Securities excluded from computation of earnings per share	6,767,930	6,203,993	6,767,930	6,203,993
Restricted stock units [Member]
Securities excluded from computation of earnings per share	186,500	72,000	186,500	72,000
Convertible Preferred Stock [Member]
Securities excluded from computation of earnings per share		10,192,700		10,192,700
Shares issuable under 2020 ESPP [Member]
Securities excluded from computation of earnings per share	18,011		18,011