Accounting policies - Revenue recognized and billed on services (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Accounting policies
Revenue recognized to date on contracts in progress	$ 122,712,011	$ 108,952,682
Amounts billed to date on contracts in progress	(113,622,422)	(101,724,459)
Retainage	8,791,564	8,087,823
Net contract asset	17,881,153	15,316,046
Contract assets	23,340,495	21,553,057
Contract liabilities	(5,459,342)	(6,237,011)
Net contract liability	$ 17,881,153	$ 15,316,046