Goodwill and Other Intangible Assets (Rollforward of Goodwill by Segment) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2017
Goodwill [Line Items]
Goodwill, gross				$ 1,342,900	$ 1,212,500
Goodwill, accumulated impairment loss				(121,500)	(74,800)
Goodwill, net	$ 1,100,350	$ 1,100,350	$ 1,137,700	1,221,440	1,137,700
Goodwill [Roll Forward]
Goodwill, net, beginning balance		1,100,350	1,137,700
Additions from new business combinations		120,400	9,800
Measurement period adjustments, net		(100)	4,600
Goodwill impairment	(47,700)		(47,700)
Currency translation adjustments		700	(4,000)
Goodwill, net, ending balance	1,100,350	1,221,440	1,100,350
Communications [Member]
Goodwill [Line Items]
Goodwill, gross				541,300	466,400
Goodwill, accumulated impairment loss				0	0
Goodwill, net	467,800	541,300	467,800	541,300	466,400
Goodwill [Roll Forward]
Goodwill, net, beginning balance		467,800	466,400
Additions from new business combinations		73,200	0
Measurement period adjustments, net		300	1,400
Goodwill impairment			0
Currency translation adjustments		0	0
Goodwill, net, ending balance	467,800	541,300	467,800
Oil and Gas [Member]
Goodwill [Line Items]
Goodwill, gross				499,100	460,400
Goodwill, accumulated impairment loss				(121,500)	(74,800)
Goodwill, net	339,600	377,600	339,600	377,600	385,600
Goodwill [Roll Forward]
Goodwill, net, beginning balance		339,600	385,600
Additions from new business combinations		37,700	0
Measurement period adjustments, net		(400)	5,700
Goodwill impairment			(47,700)
Currency translation adjustments		700	(4,000)
Goodwill, net, ending balance	339,600	377,600	339,600
Electrical Transmission [Member]
Goodwill [Line Items]
Goodwill, gross				149,900	149,900
Goodwill, accumulated impairment loss				0	0
Goodwill, net	149,900	149,900	149,900	149,900	149,900
Goodwill [Roll Forward]
Goodwill, net, beginning balance		149,900	149,900
Additions from new business combinations		0	0
Measurement period adjustments, net		0	0
Goodwill impairment			0
Currency translation adjustments		0	0
Goodwill, net, ending balance	149,900	149,900	149,900
Power Generation and Industrial [Member]
Goodwill [Line Items]
Goodwill, gross				152,600	135,800
Goodwill, accumulated impairment loss				0	0
Goodwill, net	143,100	152,600	143,100	$ 152,600	$ 135,800
Goodwill [Roll Forward]
Goodwill, net, beginning balance		143,100	135,800
Additions from new business combinations		9,500	9,800
Measurement period adjustments, net		0	(2,500)
Goodwill impairment			0
Currency translation adjustments		0	0
Goodwill, net, ending balance	$ 143,100	$ 152,600	$ 143,100