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Goodwill and Other Intangible Assets (Schedule of Goodwill by Segment) (Details) - USD ($)
$ in Thousands
Mar. 31, 2017
Dec. 31, 2016
Goodwill [Line Items]    
Goodwill, gross $ 1,067,000  
Accumulated impairment losses (70,600)  
Goodwill, net 996,383 $ 995,874
Communications [Member]    
Goodwill [Line Items]    
Goodwill, gross 420,700  
Accumulated impairment losses 0  
Goodwill, net 420,700  
Oil and Gas [Member]    
Goodwill [Line Items]    
Goodwill, gross 378,800  
Accumulated impairment losses (70,600)  
Goodwill, net 308,200  
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 117,600  
Accumulated impairment losses 0  
Goodwill, net $ 117,600