Net loss per share (Details) - shares	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Net loss per share
Number of dilutive securities excluded in the calculation of diluted net loss per share	3,412,311	3,298,100
Common stock
Net loss per share
Obligation to issue warrants, in shares	93,341	93,341
Unvested restricted common stock and restricted stock units
Net loss per share
Number of dilutive securities excluded in the calculation of diluted net loss per share	561,786	419,716
Outstanding stock options
Net loss per share
Number of dilutive securities excluded in the calculation of diluted net loss per share	2,840,525	2,802,343
Outstanding warrants
Net loss per share
Number of dilutive securities excluded in the calculation of diluted net loss per share	10,000	76,041