Accounting policies - Revenue recognized and billed on services (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2025	Dec. 31, 2024
Accounting policies
Revenue recognized to date on contracts in progress	$ 123,685,220	$ 114,590,991
Amounts billed to date on contracts in progress	(131,049,672)	(121,833,354)
Retainage	2,414,307	2,585,952
Net contract liability	(4,950,145)	(4,656,411)
Contract assets	6,731,861	4,470,243
Contract liabilities	(11,682,006)	(9,126,654)
Net contract liability	$ (4,950,145)	$ (4,656,411)