Goodwill and Other Intangible Assets (Schedule of Goodwill by Segment) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Goodwill [Line Items]
Goodwill, gross	$ 1,333,800
Accumulated impairment loss	(112,700)
Goodwill, net	1,221,147	$ 1,221,440
Communications [Member]
Goodwill [Line Items]
Goodwill, gross	541,800
Accumulated impairment loss	0
Goodwill, net	541,800
Oil and Gas [Member]
Goodwill [Line Items]
Goodwill, gross	489,300
Accumulated impairment loss	(112,700)
Goodwill, net	376,600
Electrical Transmission [Member]
Goodwill [Line Items]
Goodwill, gross	149,900
Accumulated impairment loss	0
Goodwill, net	149,900
Power Generation and Industrial [Member]
Goodwill [Line Items]
Goodwill, gross	152,800
Accumulated impairment loss	0
Goodwill, net	$ 152,800