Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Segment Reporting Information [Line Items]
Revenues from unrelated entities	$ 2,592,549	$ 2,304,049
Total revenues	2,592,549	2,304,049
Operating income (loss)	99,957	117,004
Net periodic pension (cost) income	1,169	908
Interest expense, net	(1,289)	(1,363)
Income before income taxes	99,837	116,549
Total assets	5,231,154		$ 5,441,446
UNITED STATES
Segment Reporting Information [Line Items]
Revenues from unrelated entities	2,461,052	2,177,314
Total revenues	2,461,052	2,177,314
Operating income (loss)	115,847	132,105
Total assets	4,338,452		4,206,824
United States Electrical Construction And Facilities Services [Member] | UNITED STATES
Segment Reporting Information [Line Items]
Revenues from unrelated entities	522,030	459,395
United States Mechanical Construction And Facilities Services [Member] | UNITED STATES
Segment Reporting Information [Line Items]
Revenues from unrelated entities	1,000,470	914,501
United States Building Services [Member] | UNITED STATES
Segment Reporting Information [Line Items]
Revenues from unrelated entities	627,801	568,036
United States Industrial Services [Member] | UNITED STATES
Segment Reporting Information [Line Items]
Revenues from unrelated entities	310,751	235,382
United Kingdom Building Services [Member] [Member] | UNITED KINGDOM
Segment Reporting Information [Line Items]
Revenues from unrelated entities	131,497	126,735
Operating Segments [Member] | United States Electrical Construction And Facilities Services [Member] | UNITED STATES
Segment Reporting Information [Line Items]
Revenues from unrelated entities	523,010	460,605
Total revenues	523,414	460,775
Operating income (loss)	19,993	40,252
Total assets	847,786		855,417
Operating Segments [Member] | United States Mechanical Construction And Facilities Services [Member] | UNITED STATES
Segment Reporting Information [Line Items]
Revenues from unrelated entities	1,002,738	916,172
Total revenues	1,004,856	916,722
Operating income (loss)	58,674	63,176
Total assets	1,698,791		1,672,546
Operating Segments [Member] | United States Building Services [Member] | UNITED STATES
Segment Reporting Information [Line Items]
Total revenues	652,231	590,445
Operating income (loss)	23,922	31,120
Total assets	1,132,080		1,089,844
Operating Segments [Member] | United States Industrial Services [Member] | UNITED STATES
Segment Reporting Information [Line Items]
Total revenues	324,501	245,928
Operating income (loss)	13,258	(2,443)
Total assets	659,795		589,017
Operating Segments [Member] | United Kingdom Building Services [Member] [Member] | UNITED KINGDOM
Segment Reporting Information [Line Items]
Total revenues	131,497	126,735
Operating income (loss)	10,588	9,411
Total assets	259,522		241,740
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Total revenues	(43,950)	(36,556)
Intersegment Eliminations [Member] | United States Electrical Construction And Facilities Services [Member] | UNITED STATES
Segment Reporting Information [Line Items]
Revenues from unrelated entities	(980)	(1,210)
Intersegment Eliminations [Member] | United States Mechanical Construction And Facilities Services [Member] | UNITED STATES
Segment Reporting Information [Line Items]
Revenues from unrelated entities	(2,268)	(1,671)
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Operating income (loss)	(26,478)	$ (24,512)
Total assets	$ 633,180		$ 992,882