Accounting policies - Foreign Currency (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024	Dec. 31, 2024
Foreign currency
Net foreign currency gains	$ 19,093	$ 24,807	$ 65,080	$ 65,606
Cash and cash equivalents
Cash and cash equivalents	16,900,000		16,900,000		$ 5,200,000
Deposits held in foreign bank	$ 26,400,000		$ 26,400,000		$ 7,700,000