Goodwill and Other Intangible Assets (Schedule of Goodwill by Segment) (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Goodwill [Line Items]
Goodwill, gross	$ 1,264,800
Accumulated impairment losses	(120,600)
Goodwill, net	1,144,176	$ 1,100,350
Communications [Member]
Goodwill [Line Items]
Goodwill, gross	472,800
Accumulated impairment losses	0
Goodwill, net	472,800
Oil and Gas [Member]
Goodwill [Line Items]
Goodwill, gross	499,000
Accumulated impairment losses	(120,600)
Goodwill, net	378,400
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