Goodwill and Identifiable Intangible Assets - Schedule of Goodwill (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Goodwill [Roll Forward]
Goodwill, Beginning balance	$ 964,893,000	$ 979,628,000
Acquisitions, sales and purchase price adjustments	25,994,000	42,716,000
Goodwill, intersegment transfers		0
Goodwill, Impairment	0	(57,451,000)	$ 0
Goodwill, Ending balance	990,887,000	964,893,000	979,628,000
United States electrical construction and facilities services segment
Goodwill [Roll Forward]
Goodwill, Beginning balance	125,707,000	123,600,000
Acquisitions, sales and purchase price adjustments	7,500,000	2,107,000
Goodwill, intersegment transfers		0
Goodwill, Impairment		0
Goodwill, Ending balance	133,207,000	125,707,000	123,600,000
United States Mechanical Construction And Facilities Services
Goodwill [Roll Forward]
Goodwill, Beginning balance	256,265,000	226,596,000
Acquisitions, sales and purchase price adjustments	56,000	30,969,000
Goodwill, intersegment transfers		(1,300,000)
Goodwill, Impairment		0
Goodwill, Ending balance	256,321,000	256,265,000	226,596,000
United States Building Services
Goodwill [Roll Forward]
Goodwill, Beginning balance	255,733,000	244,793,000
Acquisitions, sales and purchase price adjustments	18,438,000	9,640,000
Goodwill, intersegment transfers		1,300,000
Goodwill, Impairment		0
Goodwill, Ending balance	274,171,000	255,733,000	244,793,000
United States Industrial Services
Goodwill [Roll Forward]
Goodwill, Beginning balance	327,188,000	384,639,000
Acquisitions, sales and purchase price adjustments	0	0
Goodwill, intersegment transfers		0
Goodwill, Impairment		(57,451,000)
Goodwill, Ending balance	$ 327,188,000	$ 327,188,000	$ 384,639,000