Net loss per share (Details) - shares	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Net loss per share
Number of dilutive securities excluded in the calculation of diluted net loss per share	3,094,670	3,018,885
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	422,336	376,949
Outstanding stock options
Net loss per share
Number of dilutive securities excluded in the calculation of diluted net loss per share	2,662,334	2,565,895
Warrants
Net loss per share
Number of dilutive securities excluded in the calculation of diluted net loss per share	10,000	76,041