Goodwill and Other Intangible Assets (Schedule of Goodwill by Segment) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Goodwill [Line Items]
Goodwill, gross	$ 1,388,100
Accumulated impairment loss	(125,400)
Goodwill, net	1,262,718	$ 1,243,034
Communications [Member]
Goodwill [Line Items]
Goodwill, gross	561,900
Accumulated impairment loss	0
Goodwill, net	561,900
Clean Energy and Infrastructure [Member]
Goodwill [Line Items]
Goodwill, gross	166,400
Accumulated impairment loss	0
Goodwill, net	166,400
Oil and Gas [Member]
Goodwill [Line Items]
Goodwill, gross	509,700
Accumulated impairment loss	(125,400)
Goodwill, net	384,300
Electrical Transmission [Member]
Goodwill [Line Items]
Goodwill, gross	150,100
Accumulated impairment loss	0
Goodwill, net	$ 150,100