Stockholder's equity (deficit) - Undesignated preferred stock and Restricted common stock (Details) - $ / shares	1 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2021	Dec. 31, 2020
Restricted stock
Class of Stock
Shares issued (in shares)		226,400
Stock options vesting period	2 years	4 years
Undesignated Preferred Stock
Class of Stock
Preferred stock, par value (in dollars per share)			$ 0.0001
Preferred stock, shares issued			0	0
Preferred stock, shares outstanding			0	0
Undesignated Preferred Stock | Maximum
Class of Stock
Preferred stock, shares authorized			10,000,000