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Goodwill and Identifiable Intangible Assets - Schedule of Goodwill (Details) - USD ($)
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Goodwill [Roll Forward]      
Goodwill, Beginning balance $ 979,628,000 $ 843,170,000  
Acquisitions, sales and purchase price adjustments 42,716,000 136,458,000  
Goodwill, Transfers 0    
Goodwill, Impairment (57,451,000) 0 $ 0
Goodwill, Ending balance 964,893,000 979,628,000 843,170,000
United States electrical construction and facilities services segment      
Goodwill [Roll Forward]      
Goodwill, Beginning balance 123,600,000 3,823,000  
Acquisitions, sales and purchase price adjustments 2,107,000 119,777,000  
Goodwill, Transfers 0    
Goodwill, Impairment 0    
Goodwill, Ending balance 125,707,000 123,600,000 3,823,000
United States Mechanical Construction And Facilities Services      
Goodwill [Roll Forward]      
Goodwill, Beginning balance 226,596,000 226,071,000  
Acquisitions, sales and purchase price adjustments 30,969,000 525,000  
Goodwill, Transfers (1,300,000)    
Goodwill, Impairment 0    
Goodwill, Ending balance 256,265,000 226,596,000 226,071,000
United States Building Services      
Goodwill [Roll Forward]      
Goodwill, Beginning balance 244,793,000 228,637,000  
Acquisitions, sales and purchase price adjustments 9,640,000 16,156,000  
Goodwill, Transfers 1,300,000    
Goodwill, Impairment 0    
Goodwill, Ending balance 255,733,000 244,793,000 228,637,000
United States Industrial Services      
Goodwill [Roll Forward]      
Goodwill, Beginning balance 384,639,000 384,639,000  
Acquisitions, sales and purchase price adjustments 0 0  
Goodwill, Transfers 0    
Goodwill, Impairment (57,451,000)    
Goodwill, Ending balance $ 327,188,000 $ 384,639,000 $ 384,639,000