Stock compensation and other employee benefit plans - Outstanding option awards (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023 USD ($) $ / shares shares
Share-Based Payment Arrangement [Abstract]
Outstanding, beginning balance, Shares | shares	6,809,850
Granted, Shares | shares	450,000
Modified, Shares | shares	(1,053,750)	[1]
Exercised, Shares | shares	(717,960)
Forfeited, Shares | shares	(3,054,352)
Expired, Shares | shares	(18,262)
Outstanding, ending balance, Shares | shares	2,415,526
Vested or expected to vest in the future, Shares | shares	2,415,526
Exercisable , Shares | shares	1,958,481
Unvested and expected to vest in the future, Shares | shares	457,045
Outstanding beginning balance, Weighted average exercise price | $ / shares	$ 4.29
Granted, Weighted average exercise price | $ / shares	0.67
Modified, Weighted average exercise price | $ / shares	8.14	[1]
Exercised, Weighted average exercise price | $ / shares	0.32
Forfeited, Weighted average exercise price | $ / shares	3.38
Expired, Weighted average exercise price | $ / shares	0.48
Outstanding ending balance, Weighted average exercise price | $ / shares	1.82
Vested or expected to vest in the future, Weighted average exercise price | $ / shares	1.82
Exercisable , Weighted average exercise price | $ / shares	2.08
Unvested and expected to vest in the future, Weighted average exercise price | $ / shares	$ 0.67
Outstanding , Weighted average remaining contractual term (years)	7 years 10 days
Vested or expected to vest in the future, Weighted average remaining contractual term (in years)	7 years 10 days
Exercisable, Weighted average remaining contractual term ( in years)	6 years 4 months 13 days
Unvested and expected to vest in the future, Weighted average remaining contractual term (in years)	9 years 10 months 13 days
Outstanding , Average intrinsic value | $	$ 455
Vested or expected to vest in the future, Aggregate intrinsic value | $	455
Exercisable , Average intrinsic value | $	443
Unvested and expected to vest in the future, Aggregate intrinsic value | $	12
Stock-based compensation cost not yet recognized | $	$ 233
Weighted-average remaining expense recognition period	1 year 14 days

[1] In April 2023, we modified a grant of 2,107,500 options initially made to our former Chief Executive Officer in September 2021. The options originally granted vested after a period of time once our stock price reached certain targets and had an exercise price of $8.14 per option. The modification in April 2023 resulted in cancellation of 1,053,750 options, reset the stock price targets for vesting and reduced the exercise price to $2.48 per option, based on the estimated fair value of our stock as of the modification date. As a result of the departure of our former Chief Executive Officer during the fourth quarter of 2023, the remaining options, all of which were unvested, were forfeited.