Segment Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Revenues from unrelated entities	$ 9,903,580	$ 8,797,061	$ 9,174,611
Total revenues	9,903,580	8,797,061	9,174,611
Operating income (loss)	530,800	256,834	460,892
Restructuring expenses	0	(2,214)	(1,523)
Impairment loss on goodwill, identifiable intangible assets, and long-lived assets	0	(232,750)	0
Net periodic pension (cost) income	3,625	2,980	1,553
Interest expense	(6,071)	(9,009)	(13,821)
Interest income	949	1,521	2,265
Income before income taxes	529,303	252,326	450,889
Capital expenditures	36,192	47,969	48,432
Depreciation and amortization of property, plant and equipment	48,347	46,721	43,945
Contract assets	230,143	171,956	177,830
Contract liabilities	788,134	722,252	623,642
Long-lived assets	1,631,699	1,593,103	1,831,542
Total assets	5,441,446	5,063,840	4,830,358
UNITED STATES
Segment Reporting Information [Line Items]
Revenues from unrelated entities	9,393,629	8,366,498	8,751,352
Total revenues	9,393,629	8,366,498	8,751,352
Operating income (loss)	604,833	569,680	545,818
Capital expenditures	32,791	39,880	43,859
Depreciation and amortization of property, plant and equipment	42,396	42,106	40,196
Contract assets	199,294	141,401	152,286
Contract liabilities	754,298	692,403	601,042
Long-lived assets	1,617,762	1,576,730	1,820,489
Total assets	4,206,824	3,805,430	4,197,584
UNITED STATES | United States Electrical Construction And Facilities Services
Segment Reporting Information [Line Items]
Revenues from unrelated entities	2,015,466	1,806,092	1,961,798
UNITED STATES | United States Mechanical Construction And Facilities Services
Segment Reporting Information [Line Items]
Revenues from unrelated entities	3,922,864	3,485,495	3,340,337
UNITED STATES | United States Building Services
Segment Reporting Information [Line Items]
Revenues from unrelated entities	2,468,892	2,134,016	2,121,661
UNITED STATES | United States Industrial Services
Segment Reporting Information [Line Items]
Revenues from unrelated entities	986,407	940,895	1,327,556
UNITED KINGDOM | United Kingdom Building Services
Segment Reporting Information [Line Items]
Revenues from unrelated entities	509,951	430,563	423,259
Operating Segments [Member] | UNITED STATES | United States Electrical Construction And Facilities Services
Segment Reporting Information [Line Items]
Revenues from unrelated entities	2,018,706	1,811,217	1,965,026
Total revenues	2,019,400	1,812,445	1,965,483
Operating income (loss)	168,363	161,810	147,817
Capital expenditures	4,976	8,674	4,839
Depreciation and amortization of property, plant and equipment	7,189	6,693	6,664
Contract assets	48,161	30,728	47,522
Contract liabilities	198,247	182,228	166,448
Long-lived assets	236,813	176,708	175,038
Total assets	848,306	672,226	736,688
Operating Segments [Member] | UNITED STATES | United States Mechanical Construction And Facilities Services
Segment Reporting Information [Line Items]
Revenues from unrelated entities	3,930,753	3,492,013	3,351,918
Total revenues	3,939,753	3,502,131	3,370,960
Operating income (loss)	319,112	292,536	225,040
Capital expenditures	10,420	11,239	7,890
Depreciation and amortization of property, plant and equipment	11,130	10,683	8,764
Contract assets	87,516	68,058	61,225
Contract liabilities	406,509	386,180	317,083
Long-lived assets	506,290	512,243	530,561
Total assets	1,668,419	1,542,531	1,536,325
Operating Segments [Member] | UNITED STATES | United States Building Services
Segment Reporting Information [Line Items]
Total revenues	2,564,013	2,213,161	2,197,305
Operating income (loss)	119,024	114,159	115,432
Capital expenditures	11,236	10,372	14,370
Depreciation and amortization of property, plant and equipment	12,354	12,325	12,752
Contract assets	44,625	31,304	30,557
Contract liabilities	133,061	106,691	101,963
Long-lived assets	509,096	493,274	459,934
Total assets	1,101,082	1,040,160	1,008,263
Operating Segments [Member] | UNITED STATES | United States Industrial Services
Segment Reporting Information [Line Items]
Total revenues	1,021,217	956,373	1,351,448
Operating income (loss)	(1,666)	1,175	57,529
Capital expenditures	6,159	9,595	16,760
Depreciation and amortization of property, plant and equipment	11,723	12,405	12,016
Contract assets	18,992	11,311	12,982
Contract liabilities	16,481	17,304	15,548
Long-lived assets	365,563	394,505	654,956
Total assets	589,017	550,513	916,308
Operating Segments [Member] | UNITED KINGDOM | United Kingdom Building Services
Segment Reporting Information [Line Items]
Total revenues	509,951	430,563	423,259
Operating income (loss)	27,998	20,660	18,323
Capital expenditures	3,015	3,693	3,598
Depreciation and amortization of property, plant and equipment	3,938	3,046	2,942
Contract assets	30,849	30,555	25,544
Contract liabilities	33,836	29,849	22,600
Long-lived assets	11,402	12,017	9,622
Total assets	241,740	227,894	181,147
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Operating income (loss)	(102,031)	(98,542)	(101,726)
Capital expenditures	386	4,396	975
Depreciation and amortization of property, plant and equipment	2,013	1,569	807
Long-lived assets	2,535	4,356	1,431
Total assets	992,882	1,030,516	451,627
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Total revenues	(150,754)	(117,612)	(133,844)
Intersegment Eliminations [Member] | UNITED STATES | United States Electrical Construction And Facilities Services
Segment Reporting Information [Line Items]
Revenues from unrelated entities	(3,240)	(5,125)	(3,228)
Intersegment Eliminations [Member] | UNITED STATES | United States Mechanical Construction And Facilities Services
Segment Reporting Information [Line Items]
Revenues from unrelated entities	$ (7,889)	$ (6,518)	$ (11,581)