Goodwill and Other Intangible Assets (Schedule of Goodwill by Segment) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Goodwill [Line Items]
Goodwill, gross	$ 1,260,200
Accumulated impairment losses	(119,300)
Goodwill, net	1,140,874	$ 1,100,350
Communications [Member]
Goodwill [Line Items]
Goodwill, gross	472,600
Accumulated impairment losses	0
Goodwill, net	472,600
Oil and Gas [Member]
Goodwill [Line Items]
Goodwill, gross	494,600
Accumulated impairment losses	(119,300)
Goodwill, net	375,300
Electrical Transmission [Member]
Goodwill [Line Items]
Goodwill, gross	149,900
Accumulated impairment losses	0
Goodwill, net	149,900
Power Generation and Industrial [Member]
Goodwill [Line Items]
Goodwill, gross	143,100
Accumulated impairment losses	0
Goodwill, net	$ 143,100