Segment Information (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($) Company	Sep. 30, 2022 USD ($)	Dec. 31, 2022 USD ($)
Segment Reporting Information [Line Items]
Number of operating subsidiaries | Company			100
Revenues from unrelated entities	$ 3,207,598	$ 2,826,361	$ 9,143,652	$ 8,126,298
Total revenues	3,207,598	2,826,361	9,143,652	8,126,298
Total assets	6,224,193		6,224,193		$ 5,524,607
Net periodic pension (cost) income	(284)	1,025	(840)	3,288
Interest expense, net	(90)	(3,194)	(4,614)	(6,234)
Operating income (loss)	234,983	150,094	586,560	387,695
Impairment loss on long-lived assets	(2,350)	0	(2,350)	0
Income before income taxes	234,609	147,925	581,106	384,749
UNITED STATES
Segment Reporting Information [Line Items]
Revenues from unrelated entities	3,096,872	2,708,660	8,816,009	7,762,552
Total revenues	3,096,872	2,708,660	8,816,009	7,762,552
Total assets	5,335,493		5,335,493		4,672,469
Operating income (loss)	258,585	170,707	662,591	443,213
United States Electrical Construction And Facilities Services [Member] | UNITED STATES
Segment Reporting Information [Line Items]
Revenues from unrelated entities	697,406	633,383	2,020,319	1,719,525
United States Mechanical Construction And Facilities Services [Member] | UNITED STATES
Segment Reporting Information [Line Items]
Revenues from unrelated entities	1,329,600	1,108,655	3,602,271	3,158,948
United States Building Services [Member] | UNITED STATES
Segment Reporting Information [Line Items]
Revenues from unrelated entities	817,718	719,383	2,318,105	2,041,555
United States Industrial Services [Member] | UNITED STATES
Segment Reporting Information [Line Items]
Revenues from unrelated entities	252,148	247,239	875,314	842,524
United Kingdom Building Services [Member] [Member] | UNITED KINGDOM
Segment Reporting Information [Line Items]
Revenues from unrelated entities	110,726	117,701	327,643	363,746
Operating Segments [Member] | United States Electrical Construction And Facilities Services [Member] | UNITED STATES
Segment Reporting Information [Line Items]
Revenues from unrelated entities	697,766	634,327	2,022,002	1,723,090
Total revenues	697,897	634,957	2,022,557	1,724,400
Total assets	1,173,992		1,173,992		1,078,405
Operating income (loss)	63,127	35,558	154,365	90,646
Operating Segments [Member] | United States Mechanical Construction And Facilities Services [Member] | UNITED STATES
Segment Reporting Information [Line Items]
Revenues from unrelated entities	1,332,747	1,111,900	3,608,595	3,167,091
Total revenues	1,342,149	1,125,162	3,650,875	3,187,117
Total assets	2,159,947		2,159,947		1,835,001
Operating income (loss)	138,476	90,500	344,550	225,545
Operating Segments [Member] | United States Building Services [Member] | UNITED STATES
Segment Reporting Information [Line Items]
Total revenues	846,400	744,801	2,397,944	2,116,385
Total assets	1,415,194		1,415,194		1,206,518
Operating income (loss)	57,156	46,041	140,943	108,698
Operating Segments [Member] | United States Industrial Services [Member] | UNITED STATES
Segment Reporting Information [Line Items]
Total revenues	252,244	266,182	883,808	878,123
Total assets	586,360		586,360		552,545
Operating income (loss)	(174)	(1,392)	22,733	18,324
Operating Segments [Member] | United Kingdom Building Services [Member] [Member] | UNITED KINGDOM
Segment Reporting Information [Line Items]
Total revenues	110,726	117,701	327,643	363,746
Total assets	262,629		262,629		255,547
Operating income (loss)	8,869	8,369	20,220	25,372
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Total assets	626,071		626,071		$ 596,591
Operating income (loss)	(30,121)	(28,982)	(93,901)	(80,890)
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Total revenues	(41,818)	(62,442)	(139,175)	(143,473)
Intersegment Eliminations [Member] | United States Electrical Construction And Facilities Services [Member] | UNITED STATES
Segment Reporting Information [Line Items]
Revenues from unrelated entities	(360)	(944)	(1,683)	(3,565)
Intersegment Eliminations [Member] | United States Mechanical Construction And Facilities Services [Member] | UNITED STATES
Segment Reporting Information [Line Items]
Revenues from unrelated entities	$ (3,147)	$ (3,245)	$ (6,324)	$ (8,143)