Earnings (loss) per share - Schedule of basic and diluted net loss per common stock (Detail) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Securities excluded from computation of earnings per share	5,762,348	2,631,097	5,762,348	2,631,097
Outstanding stock options [Member]
Securities excluded from computation of earnings per share	5,613,337	2,631,097	5,613,337	2,631,097
Restricted stock units [Member]
Securities excluded from computation of earnings per share	131,000		131,000
Shares issuable under 2020 ESPP [Member]
Securities excluded from computation of earnings per share	18,011		18,011