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Revenue from Contracts with Customers (Details) - USD ($)
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Business Acquisition [Line Items]    
Performance obligation satisfied in previous period $ 0 $ 7,300,000
Change in estimate of transaction price 0 0
Loss on contracts 0  
Unbilled revenues for unapproved change orders 33,100,000 25,200,000
Accounts receivable, unapproved contract claims 0 0
Accounts receivable, contractually billed amounts on contracts related to unapproved contract claims 89,000,000.0 96,100,000
Net billings in excess of costs 406,552,000 359,157,000
Change in net contract liabilities 51,800,000  
Change in net billings in excess of costs 47,400,000  
Contract asset impairment 0  
Accounts receivable, retainage $ 298,500,000 254,600,000
Accounts receivable, retainage estimated to be collected in next fiscal year 88.00%  
Accounts payable, retainage $ 64,700,000 43,300,000
Accounts payable, retainage estimated to be paid in next fiscal year 86.00%  
Remaining performance obligations $ 4,036,364,000  
2019 Acquisitions    
Business Acquisition [Line Items]    
Increase (decrease) in contract assets from acquisitions 8,200,000  
Increase (decrease) in contract liabilities from acquisitions $ 29,000,000.0  
United States Electrical Construction And Facilities Services | Transportation Sector [Member]    
Business Acquisition [Line Items]    
Loss on contracts   $ 10,000,000.0