Revenue - Disaggregation of revenue by customer type and contract type (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Disaggregation of Revenue
Revenue	$ 1,649,086	$ 1,529,486	$ 4,625,508	$ 4,199,760
Fixed price
Disaggregation of Revenue
Revenue	669,318	642,339	1,941,110	1,838,526
Unit price
Disaggregation of Revenue
Revenue	616,768	574,429	1,607,797	1,577,748
Cost reimbursable
Disaggregation of Revenue
Revenue	363,000	312,718	1,076,601	783,486
MSA
Disaggregation of Revenue
Revenue	625,016	583,785	1,673,451	1,577,291
Non-MSA
Disaggregation of Revenue
Revenue	1,024,070	945,701	2,952,057	2,622,469
Intersegment eliminations
Disaggregation of Revenue
Revenue	(28,012)	(8,921)	(81,382)	(28,019)
Intersegment eliminations | Fixed price
Disaggregation of Revenue
Revenue	(27,748)	(1,660)	(79,233)	(7,719)
Intersegment eliminations | Unit price
Disaggregation of Revenue
Revenue	(128)	(5,444)	(1,893)	(17,309)
Intersegment eliminations | Cost reimbursable
Disaggregation of Revenue
Revenue	(136)	(1,817)	(256)	(2,991)
Intersegment eliminations | MSA
Disaggregation of Revenue
Revenue	(20)	(768)	(258)	(5,385)
Intersegment eliminations | Non-MSA
Disaggregation of Revenue
Revenue	(27,992)	(8,153)	(81,124)	(22,634)
Utilities | Operating Segment
Disaggregation of Revenue
Revenue	666,240	650,664	1,774,962	1,833,665
Utilities | Operating Segment | Fixed price
Disaggregation of Revenue
Revenue	88,167	107,024	268,738	294,709
Utilities | Operating Segment | Unit price
Disaggregation of Revenue
Revenue	437,493	411,636	1,122,898	1,146,601
Utilities | Operating Segment | Cost reimbursable
Disaggregation of Revenue
Revenue	140,580	132,004	383,326	392,355
Utilities | Operating Segment | MSA
Disaggregation of Revenue
Revenue	552,741	505,728	1,430,696	1,359,495
Utilities | Operating Segment | Non-MSA
Disaggregation of Revenue
Revenue	113,499	144,936	344,266	474,170
Energy | Operating Segment
Disaggregation of Revenue
Revenue	1,010,858	887,743	2,931,928	2,394,114
Energy | Operating Segment | Fixed price
Disaggregation of Revenue
Revenue	608,899	536,975	1,751,605	1,551,536
Energy | Operating Segment | Unit price
Disaggregation of Revenue
Revenue	179,403	168,237	486,792	448,456
Energy | Operating Segment | Cost reimbursable
Disaggregation of Revenue
Revenue	222,556	182,531	693,531	394,122
Energy | Operating Segment | MSA
Disaggregation of Revenue
Revenue	72,295	78,825	243,013	223,181
Energy | Operating Segment | Non-MSA
Disaggregation of Revenue
Revenue	$ 938,563	$ 808,918	$ 2,688,915	$ 2,170,933