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Business, Basis of Presentation and Significant Accounting Policies (Narrative) (Details)
$ in Millions
3 Months Ended
Mar. 31, 2021
USD ($)
numberOfSegments
Mar. 31, 2020
USD ($)
Dec. 31, 2020
USD ($)
Segment Reporting, Disclosure of Entity's Reportable Segments [Abstract]      
Number of reportable segments | numberOfSegments 5    
Accrued payroll taxes $ 59.0    
Revenue [Line Items]      
Revenue recognition, performance obligations satisfied in previous periods, revenue recognized (in dollars) 13.8 $ 17.8  
Contract with customer, unapproved change orders and/or claims, amount (in dollars) 59.0   $ 51.0
Mobilization Costs      
Revenue [Line Items]      
Mobilization costs $ 3.7   $ 5.5
Maximum [Member]      
Revenue [Line Items]      
Revenue recognition, changes In contract estimates, cost-to-cost method, financial effect, percentage 5.00% 5.00%  
Change order or claim approval process, term within which expected to be completed (in years) 1 year    
Revenue Benchmark [Member] | Concentration Risk from Type of Arrangement [Member] | Master Service and Other Service Agreements [Member]      
Revenue [Line Items]      
Concentration risk, percentage of total 28.00% 42.00%  
Revenue Benchmark [Member] | Concentration Risk from Type of Arrangement [Member] | Master Service and Other Service Agreements [Member] | Point in Time [Member]      
Revenue [Line Items]      
Concentration risk, percentage of total 5.00% 6.00%