Stockholders' equity - SARs Activity (Details) - Stock Appreciation Rights - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2022	Dec. 31, 2021
Outstanding
Outstanding, beginning balance (in shares)	106,155
Granted (in shares)	0
Exercised (in shares)	0
Canceled (in shares)	(532)
Outstanding, ending balance (in shares)	105,623	106,155
Weighted Average Exercise Price
Outstanding, beginning balance (in USD per share)	$ 8.45
Granted (in USD per share)	0
Exercised (in USD per share)	0
Canceled (in USD per share)	10.02
Outstanding, ending balance (in USD per share)	$ 8.45	$ 8.45
Outstanding, Weighted Average Remaining Contractual Term (in years)	7 years 11 months 12 days	8 years 3 months
Outstanding, Aggregate Intrinsic Value	$ 595	$ 1,267
Vested and Expected to Vest, Awards Outstanding (in shares)	105,623
Vested and Expected to Vest, Weighted Average Exercise Price (in USD per shares)	$ 8.45
Vested and Expected to Vest, Weighted Average Remaining Contractual Term (in years)	7 years 11 months 12 days
Vested and Expected to Vest, Aggregate Intrinsic Value	$ 595
Exercisable, Awards Outstanding (in shares)	55,585
Exercisable, Weighted Average Exercise Price (in USD per share)	$ 5.57
Exercisable, Weighted Average Remaining Contractual Term (in years)	7 years 7 months 9 days
Exercisable, Aggregate Intrinsic Value	$ 384