Goodwill and Other Intangible Assets (Schedule of Goodwill by Segment) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Goodwill [Line Items]
Goodwill, gross	$ 1,210,900
Accumulated impairment losses	(75,400)
Goodwill, net	1,135,450	$ 995,874
Communications [Member]
Goodwill [Line Items]
Goodwill, gross	462,400
Accumulated impairment losses	0
Goodwill, net	462,400
Oil and Gas [Member]
Goodwill [Line Items]
Goodwill, gross	461,600
Accumulated impairment losses	(75,400)
Goodwill, net	386,200
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	137,000
Accumulated impairment losses	0
Goodwill, net	$ 137,000

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=77989000&loc=SL49117168-202975

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