Revenue from Contracts with Customers - Schedule of Disaggregation of Revenues (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Revenues from unrelated entities		$ 2,437,666	$ 2,014,021	$ 4,741,715	$ 4,313,853
UNITED STATES
Disaggregation of Revenue [Line Items]
Revenues from unrelated entities		2,307,792	1,920,904	4,485,106	4,108,359
United States Electrical Construction And Facilities Services [Member] | UNITED STATES
Disaggregation of Revenue [Line Items]
Revenues from unrelated entities		489,487	410,388	945,655	872,191
United States Electrical Construction And Facilities Services [Member] | UNITED STATES | Operating Segments [Member]
Disaggregation of Revenue [Line Items]
Revenues from unrelated entities		490,080	411,222	947,443	873,837
United States Electrical Construction And Facilities Services [Member] | UNITED STATES | Operating Segments [Member] | Commercial Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenues from unrelated entities		$ 253,774	$ 212,318	$ 498,757	$ 452,164
Percent of individual segment		52.00%	52.00%	53.00%	52.00%
United States Electrical Construction And Facilities Services [Member] | UNITED STATES | Operating Segments [Member] | Institutional Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenues from unrelated entities		$ 52,587	$ 32,691	$ 95,716	$ 70,084
Percent of individual segment		11.00%	8.00%	10.00%	8.00%
United States Electrical Construction And Facilities Services [Member] | UNITED STATES | Operating Segments [Member] | Hospitality Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenues from unrelated entities		$ 4,100	$ 4,899	$ 8,764	$ 9,981
Percent of individual segment		1.00%	1.00%	1.00%	1.00%
United States Electrical Construction And Facilities Services [Member] | UNITED STATES | Operating Segments [Member] | Manufacturing Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenues from unrelated entities		$ 51,998	$ 55,910	$ 100,421	$ 122,753
Percent of individual segment		10.00%	13.00%	10.00%	14.00%
United States Electrical Construction And Facilities Services [Member] | UNITED STATES | Operating Segments [Member] | Healthcare Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenues from unrelated entities		$ 25,678	$ 16,025	$ 45,092	$ 35,250
Percent of individual segment		5.00%	4.00%	5.00%	4.00%
United States Electrical Construction And Facilities Services [Member] | UNITED STATES | Operating Segments [Member] | Transportation Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenues from unrelated entities		$ 53,179	$ 47,966	$ 95,210	$ 92,146
Percent of individual segment		11.00%	12.00%	10.00%	10.00%
United States Electrical Construction And Facilities Services [Member] | UNITED STATES | Operating Segments [Member] | Water and Wastewater Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenues from unrelated entities		$ 1,877	$ 1,907	$ 5,528	$ 4,236
Percent of individual segment		1.00%	1.00%	1.00%	1.00%
United States Electrical Construction And Facilities Services [Member] | UNITED STATES | Operating Segments [Member] | Short Duration Projects [Member]
Disaggregation of Revenue [Line Items]
Revenues from unrelated entities	[1]	$ 37,484	$ 33,507	$ 81,284	$ 73,777
Percent of individual segment		7.00%	8.00%	8.00%	8.00%
United States Electrical Construction And Facilities Services [Member] | UNITED STATES | Operating Segments [Member] | Service Work [Member]
Disaggregation of Revenue [Line Items]
Revenues from unrelated entities		$ 9,403	$ 5,999	$ 16,671	$ 13,446
Percent of individual segment		2.00%	1.00%	2.00%	2.00%
United States Electrical Construction And Facilities Services [Member] | UNITED STATES | Intersegment Eliminations [Member]
Disaggregation of Revenue [Line Items]
Revenues from unrelated entities		$ (593)	$ (834)	$ (1,788)	$ (1,646)
United States Mechanical Construction And Facilities Services [Member] | UNITED STATES
Disaggregation of Revenue [Line Items]
Revenues from unrelated entities		958,686	790,441	1,862,611	1,624,553
United States Mechanical Construction And Facilities Services [Member] | UNITED STATES | Operating Segments [Member]
Disaggregation of Revenue [Line Items]
Revenues from unrelated entities		960,423	791,411	1,865,969	1,627,407
United States Mechanical Construction And Facilities Services [Member] | UNITED STATES | Operating Segments [Member] | Commercial Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenues from unrelated entities		$ 397,482	$ 273,434	$ 764,157	$ 578,124
Percent of individual segment		41.00%	35.00%	41.00%	36.00%
United States Mechanical Construction And Facilities Services [Member] | UNITED STATES | Operating Segments [Member] | Institutional Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenues from unrelated entities		$ 71,464	$ 99,829	$ 140,768	$ 176,826
Percent of individual segment		7.00%	13.00%	7.00%	11.00%
United States Mechanical Construction And Facilities Services [Member] | UNITED STATES | Operating Segments [Member] | Hospitality Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenues from unrelated entities		$ 11,258	$ 9,098	$ 19,787	$ 16,812
Percent of individual segment		1.00%	1.00%	1.00%	1.00%
United States Mechanical Construction And Facilities Services [Member] | UNITED STATES | Operating Segments [Member] | Manufacturing Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenues from unrelated entities		$ 102,224	$ 100,608	$ 207,651	$ 216,190
Percent of individual segment		11.00%	13.00%	11.00%	13.00%
United States Mechanical Construction And Facilities Services [Member] | UNITED STATES | Operating Segments [Member] | Healthcare Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenues from unrelated entities		$ 121,745	$ 80,528	$ 234,530	$ 168,587
Percent of individual segment		13.00%	10.00%	13.00%	10.00%
United States Mechanical Construction And Facilities Services [Member] | UNITED STATES | Operating Segments [Member] | Transportation Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenues from unrelated entities		$ 20,704	$ 19,669	$ 39,121	$ 34,015
Percent of individual segment		2.00%	2.00%	2.00%	2.00%
United States Mechanical Construction And Facilities Services [Member] | UNITED STATES | Operating Segments [Member] | Water and Wastewater Market Sector [Member]
Disaggregation of Revenue [Line Items]
Revenues from unrelated entities		$ 44,702	$ 45,606	$ 88,550	$ 86,119
Percent of individual segment		5.00%	6.00%	5.00%	5.00%
United States Mechanical Construction And Facilities Services [Member] | UNITED STATES | Operating Segments [Member] | Short Duration Projects [Member]
Disaggregation of Revenue [Line Items]
Revenues from unrelated entities	[1]	$ 83,604	$ 73,955	$ 172,387	$ 171,157
Percent of individual segment		9.00%	9.00%	9.00%	11.00%
United States Mechanical Construction And Facilities Services [Member] | UNITED STATES | Operating Segments [Member] | Service Work [Member]
Disaggregation of Revenue [Line Items]
Revenues from unrelated entities		$ 107,240	$ 88,684	$ 199,018	$ 179,577
Percent of individual segment		11.00%	11.00%	11.00%	11.00%
United States Mechanical Construction And Facilities Services [Member] | UNITED STATES | Intersegment Eliminations [Member]
Disaggregation of Revenue [Line Items]
Revenues from unrelated entities		$ (1,737)	$ (970)	$ (3,358)	$ (2,854)
United States Building Services [Member] | UNITED STATES
Disaggregation of Revenue [Line Items]
Revenues from unrelated entities		624,456	478,982	1,206,295	1,006,593
United States Building Services [Member] | UNITED STATES | Commercial Site-Based Services [Member]
Disaggregation of Revenue [Line Items]
Revenues from unrelated entities		$ 152,851	$ 132,078	$ 328,498	$ 275,516
Percent of individual segment		25.00%	28.00%	27.00%	27.00%
United States Building Services [Member] | UNITED STATES | Government Site-Based Services [Member]
Disaggregation of Revenue [Line Items]
Revenues from unrelated entities		$ 46,587	$ 38,419	$ 87,659	$ 81,336
Percent of individual segment		7.00%	8.00%	7.00%	8.00%
United States Building Services [Member] | UNITED STATES | Mobile Mechanical Services [Member]
Disaggregation of Revenue [Line Items]
Revenues from unrelated entities		$ 398,813	$ 289,531	$ 733,763	$ 602,450
Percent of individual segment		64.00%	60.00%	61.00%	60.00%
United States Building Services [Member] | UNITED STATES | Energy Services [Member]
Disaggregation of Revenue [Line Items]
Revenues from unrelated entities		$ 26,205	$ 18,954	$ 56,375	$ 47,291
Percent of individual segment		4.00%	4.00%	5.00%	5.00%
United States Industrial Services [Member] | UNITED STATES
Disaggregation of Revenue [Line Items]
Revenues from unrelated entities		$ 235,163	$ 241,093	$ 470,545	$ 605,022
United States Industrial Services [Member] | UNITED STATES | Field Services [Member]
Disaggregation of Revenue [Line Items]
Revenues from unrelated entities		$ 208,797	$ 206,288	$ 416,351	$ 529,942
Percent of individual segment		89.00%	86.00%	88.00%	88.00%
United States Industrial Services [Member] | UNITED STATES | Shop Services [Member]
Disaggregation of Revenue [Line Items]
Revenues from unrelated entities		$ 26,366	$ 34,805	$ 54,194	$ 75,080
Percent of individual segment		11.00%	14.00%	12.00%	12.00%
United Kingdom Building Services [Member] [Member] | UNITED KINGDOM
Disaggregation of Revenue [Line Items]
Revenues from unrelated entities		$ 129,874	$ 93,117	$ 256,609	$ 205,494
United Kingdom Building Services [Member] [Member] | UNITED KINGDOM | Service Work [Member]
Disaggregation of Revenue [Line Items]
Revenues from unrelated entities		$ 66,572	$ 51,139	$ 128,563	$ 106,245
Percent of individual segment		51.00%	55.00%	50.00%	52.00%
United Kingdom Building Services [Member] [Member] | UNITED KINGDOM | Project Work [Member]
Disaggregation of Revenue [Line Items]
Revenues from unrelated entities		$ 63,302	$ 41,978	$ 128,046	$ 99,249
Percent of individual segment		49.00%	45.00%	50.00%	48.00%

[1] Represents those projects which generally are completed within three months or less.