Stock-based compensation - Shares Authorized Under Stock Option Plan (Details)	12 Months Ended
	Dec. 31, 2023 $ / shares shares
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Shares outstanding | shares	217,250
Weighted Average Remaining Contractual Life	2 years 21 days
Weighted Average Exercise Price (in dollars per share)	$ 2.21
$1.00 - 1.50
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Option, exercise price range, lower range limit	1.00
Option, exercise price range, upper range limit	$ 1.50
Shares outstanding | shares	2,000
Weighted Average Remaining Contractual Life	2 years 10 months 6 days
Weighted Average Exercise Price (in dollars per share)	$ 1.49
$1.51 - 2.00
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Option, exercise price range, lower range limit	1.51
Option, exercise price range, upper range limit	$ 2.00
Shares outstanding | shares	116,500
Weighted Average Remaining Contractual Life	2 years 3 months 25 days
Weighted Average Exercise Price (in dollars per share)	$ 1.89
$2.01 - 2.50
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Option, exercise price range, lower range limit	2.01
Option, exercise price range, upper range limit	$ 2.50
Shares outstanding | shares	84,500
Weighted Average Remaining Contractual Life	1 year 4 months 9 days
Weighted Average Exercise Price (in dollars per share)	$ 2.07
$2.51 - 8.60
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Option, exercise price range, lower range limit	2.51
Option, exercise price range, upper range limit	$ 8.60
Shares outstanding | shares	14,250
Weighted Average Remaining Contractual Life	3 years 11 months 1 day
Weighted Average Exercise Price (in dollars per share)	$ 5.69