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Goodwill and Other Intangible Assets (2018 Acquisitions) (Narrative) (Details) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Business Combinations [Line Items]    
Business combinations, contingent consideration liabilities, range of potential undiscounted earn-out liabilities, high (in dollars) $ 196.0  
Business combinations, contingent consideration liabilities, range of potential earn-out liabilities, maximum unlimited there is no maximum payment amount  
Construction Management Firm Specializing in Steel Building Systems [Member]    
Business Combinations [Line Items]    
Business combinations, percentage of interests acquired 100.00%  
2018 Acquisitions [Member]    
Business Combinations [Line Items]    
Business combinations, cash paid (in dollars)   $ 6.8
Business combinations, contingent consideration, earn-out liabilities $ 1.5  
Business combinations, contingent consideration liabilities, range of potential undiscounted earn-out liabilities, high (in dollars) $ 6.0  
Business combinations, contingent consideration liabilities, range of potential earn-out liabilities, maximum unlimited there is no maximum payment amount