Accounting policies - Revenue recognized and billed on services (Details) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2025	Dec. 31, 2024
Accounting policies
Revenue recognized to date on contracts in progress	$ 112,905,596	$ 114,590,991
Amounts billed to date on contracts in progress	(122,213,705)	(121,833,354)
Retainage	2,168,473	2,585,952
Net contract liability	(7,139,636)	(4,656,411)
Contract assets	5,759,030	4,470,243
Contract liabilities	(12,898,666)	(9,126,654)
Net contract liability	$ (7,139,636)	$ (4,656,411)