Goodwill and Other Intangible Assets (Schedule of Goodwill by Segment) (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Goodwill [Line Items]
Goodwill, gross	$ 1,112,800
Accumulated impairment losses	(72,500)
Goodwill, net	1,040,302	$ 995,874
Communications [Member]
Goodwill [Line Items]
Goodwill, gross	463,100
Accumulated impairment losses	0
Goodwill, net	463,100
Oil and Gas [Member]
Goodwill [Line Items]
Goodwill, gross	382,200
Accumulated impairment losses	(72,500)
Goodwill, net	309,700
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	117,600
Accumulated impairment losses	0
Goodwill, net	$ 117,600