Accounting policies - Cash and cash equivalents (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Net foreign currency gains	$ 84,678	$ 41,750
Cash and cash equivalents	11,912,286	5,484,328
Deposits	16,900,000
Cash held in foreign bank accounts	24,200,000
Deposits held in foreign bank	3,000,000.0	5,700,000
Certificate of deposit
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	$ 5,100,000	$ 5,000,000.0