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Business, Basis of Presentation and Significant Accounting Policies (Revenue Recognition) (Narrative) (Details) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2021
Jun. 30, 2020
Jun. 30, 2021
Jun. 30, 2020
Dec. 31, 2020
Revenue [Line Items]          
Revenue recognition, performance obligations satisfied in previous periods, revenue recognized (in dollars) $ 30.5 $ 5.4 $ 37.0 $ 15.8  
Revenue recognition, remaining performance obligations, contract price allocated (in dollars) 5,200.0   5,200.0    
Contract with customer, unapproved change orders and/or claims, amount (in dollars) 97.0   97.0   $ 51.0
Mobilization Costs          
Revenue [Line Items]          
Mobilization costs $ 2.7   $ 2.7   $ 5.5
Maximum          
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 | Concentration Risk from Type of Arrangement | Master Service and Other Service Agreements          
Revenue [Line Items]          
Concentration risk, percentage of total 32.00% 36.00% 31.00% 39.00%  
Revenue Benchmark | Concentration Risk from Type of Arrangement | Master Service and Other Service Agreements | Point in Time          
Revenue [Line Items]          
Concentration risk, percentage of total 4.00% 5.00% 4.00% 5.00%  
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-07-01          
Revenue [Line Items]          
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period 6 months   6 months    
Revenue recognition, remaining performance obligations, contract price allocated (in dollars) $ 2,900.0   $ 2,900.0