Accounting policies - Revenue recognized and billed on services (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2025	Dec. 31, 2024
Accounting policies
Revenue recognized to date on contracts in progress	$ 111,400,995	$ 114,590,991
Amounts billed to date on contracts in progress	(117,315,578)	(121,833,354)
Retainage	3,030,454	2,585,952
Net contract asset /(liability)	(2,884,129)	(4,656,411)
Contract assets	9,517,668	4,470,243
Contract liabilities	(12,401,797)	(9,126,654)
Net contract asset /(liability)	$ (2,884,129)	$ (4,656,411)