Equity incentive plans - SARs Activity (Details) - Stock Appreciation Rights - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Outstanding
Outstanding, beginning balance (in shares)	95,475
Granted (in shares)	17,755
Exercised (in shares)	(458)
Canceled (in shares)	(6,617)
Outstanding, ending balance (in shares)	106,155	95,475
Weighted Average Exercise Price
Outstanding, beginning balance (in USD per share)	$ 5.64
Granted (in USD per share)	22.56
Exercised (in USD per share)	3.12
Canceled (in USD per share)	6.04
Outstanding, ending balance (in USD per share)	$ 8.45	$ 5.64
Outstanding, Weighted Average Remaining Contractual Term (in years)	8 years 3 months	9 years
Outstanding, Aggregate Intrinsic Value	$ 1,267	$ 586
Vested and Expected to Vest, Awards Outstanding (in shares)	106,155
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)	8 years 3 months
Vested and Expected to Vest, Aggregate Intrinsic Value	$ 1,267
Exercisable, Awards Outstanding (in shares)	48,560
Exercisable, Weighted Average Exercise Price (in USD per share)	$ 5.34
Exercisable, Weighted Average Remaining Contractual Term (in years)	7 years 10 months 24 days
Exercisable, Aggregate Intrinsic Value	$ 690