Accounting policies - Cash and cash equivalents (Details) - USD ($)	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Net foreign currency gains	$ 74,993	$ 84,678	$ 41,750
Cash and cash equivalents	35,038,857	11,912,286
Deposits	54,700,000
Cash held in foreign bank accounts	34,100,000
Deposits held in foreign bank	7,700,000	3,000,000
Certificate of deposit
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	$ 5,200,000	$ 5,100,000