Revenue - Disaggregation of revenue by customer type and contract type (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Disaggregation of Revenue
Revenue	$ 1,563,715	$ 1,413,377	$ 2,976,422	$ 2,670,273
Fixed price
Disaggregation of Revenue
Revenue	602,441	583,424	1,271,792	1,196,186
Unit price
Disaggregation of Revenue
Revenue	552,568	554,478	991,029	1,003,318
Cost reimbursable
Disaggregation of Revenue
Revenue	408,706	275,475	713,601	470,769
MSA
Disaggregation of Revenue
Revenue	574,366	544,387	1,048,436	993,506
Non-MSA
Disaggregation of Revenue
Revenue	989,349	868,990	1,927,986	1,676,767
Intersegment Eliminations
Disaggregation of Revenue
Revenue	(30,575)	(14,576)	(53,370)	(19,099)
Intersegment Eliminations | Fixed price
Disaggregation of Revenue
Revenue	(30,536)	(3,310)	(51,485)	(6,059)
Intersegment Eliminations | Unit price
Disaggregation of Revenue
Revenue	(12)	(11,008)	(1,765)	(11,866)
Intersegment Eliminations | Cost reimbursable
Disaggregation of Revenue
Revenue	(27)	(258)	(120)	(1,174)
Intersegment Eliminations | MSA
Disaggregation of Revenue
Revenue	(44)	(2,950)	(238)	(4,617)
Intersegment Eliminations | Non-MSA
Disaggregation of Revenue
Revenue	(30,531)	(11,626)	(53,132)	(14,482)
Utilities | Operating Segment
Disaggregation of Revenue
Revenue	620,798	649,238	1,108,722	1,183,001
Utilities | Operating Segment | Fixed price
Disaggregation of Revenue
Revenue	93,571	101,738	180,571	187,685
Utilities | Operating Segment | Unit price
Disaggregation of Revenue
Revenue	387,980	411,594	685,405	734,965
Utilities | Operating Segment | Cost reimbursable
Disaggregation of Revenue
Revenue	139,247	135,906	242,746	260,351
Utilities | Operating Segment | MSA
Disaggregation of Revenue
Revenue	496,458	480,131	877,956	853,767
Utilities | Operating Segment | Non-MSA
Disaggregation of Revenue
Revenue	124,340	169,107	230,766	329,234
Energy | Operating Segment
Disaggregation of Revenue
Revenue	973,492	778,715	1,921,070	1,506,371
Energy | Operating Segment | Fixed price
Disaggregation of Revenue
Revenue	539,406	484,996	1,142,706	1,014,560
Energy | Operating Segment | Unit price
Disaggregation of Revenue
Revenue	164,600	153,892	307,389	280,219
Energy | Operating Segment | Cost reimbursable
Disaggregation of Revenue
Revenue	269,486	139,827	470,975	211,592
Energy | Operating Segment | MSA
Disaggregation of Revenue
Revenue	77,952	67,206	170,718	144,356
Energy | Operating Segment | Non-MSA
Disaggregation of Revenue
Revenue	$ 895,540	$ 711,509	$ 1,750,352	$ 1,362,015