Stock-based compensation - Stock Option Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Shares
Exercised (in shares)		(161,646)
Wtd. Avg. Exercise Price
Outstanding as of end of period (in dollars per share)	$ 2.21
Service vesting-based stock options
Shares
Outstanding as of beginning of period (in shares)	456,293	624,531
Exercised (in shares)	(239,043)	(161,646)
Expired (in shares)	0	(6,592)
Outstanding at end of year (in shares)	217,250	456,293
Stock options exercisable at year end (in shares)	217,250	456,293
Wtd. Avg. Exercise Price
Outstanding as of beginning of period (in dollars per share)	$ 2.17	$ 2.13
Exercised (in dollars per share)	2.12	2.00
Expired (in dollars per share)	0	3.22
Outstanding as of end of period (in dollars per share)	2.21	2.17
Stock options exercisable at year end (in dollars per share)	$ 2.21	$ 2.17