Accounting policies - Cash and cash equivalents (Details) - USD ($)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2023
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Net foreign currency gains	$ 41,750	$ 32,594
Cash and cash equivalents	5,484,328	7,738,216
Deposits	12,500,000
Cash held in foreign bank accounts	36,600,000
Deposits held in foreign bank	5,700,000	3,900,000
Certificate of deposit
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	$ 5,000,000.0	7,400,000
Certificate of deposit | Bahamas [Member]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents		$ 2,500,000	$ 0