Goodwill and Other Intangible Assets (Schedule of Goodwill by Segment) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Goodwill [Line Items]
Goodwill, gross	$ 1,350,300
Accumulated impairment loss	(118,600)
Goodwill, net	1,231,717	$ 1,221,440
Communications [Member]
Goodwill [Line Items]
Goodwill, gross	551,400
Accumulated impairment loss	0
Goodwill, net	551,400
Oil and Gas [Member]
Goodwill [Line Items]
Goodwill, gross	496,000
Accumulated impairment loss	(118,600)
Goodwill, net	377,400
Electrical Transmission [Member]
Goodwill [Line Items]
Goodwill, gross	150,100
Accumulated impairment loss	0
Goodwill, net	150,100
Clean Energy and Infrastructure [Member]
Goodwill [Line Items]
Goodwill, gross	152,800
Accumulated impairment loss	0
Goodwill, net	$ 152,800