Accounting policies - Foreign Currency (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024	Dec. 31, 2024
Foreign currency
Net foreign currency gains	$ 16,345	$ 16,602	$ 45,987	$ 40,799
Cash and cash equivalents
Cash and cash equivalents	16,900,000		16,900,000		$ 5,200,000
Deposits held in foreign bank	$ 14,200,000		$ 14,200,000		$ 7,700,000