Net loss per common stock - Schedule of basic and diluted net loss per common stock (Detail) - shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Securities excluded from computation of earnings per share	5,912,538	2,897,294	2,069,167
Outstanding stock options [Member]
Securities excluded from computation of earnings per share	5,840,538	2,897,294	2,069,167
Restricted stock units [Member]
Securities excluded from computation of earnings per share	72,000