Net loss per share (Details) - shares	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Net loss per share
Number of dilutive securities excluded in the calculation of diluted net loss per share	3,234,437	3,153,098
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	479,996	436,985
Outstanding stock options
Net loss per share
Number of dilutive securities excluded in the calculation of diluted net loss per share	2,744,441	2,640,072
Outstanding warrants
Net loss per share
Number of dilutive securities excluded in the calculation of diluted net loss per share	10,000	76,041