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Acquisitions and Dispositions Acquisitions and Dispositions - Dispositions (Details) - USD ($)
$ in Millions
3 Months Ended 12 Months Ended
Jun. 01, 2018
Jun. 30, 2018
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]          
Gain on sale of business     $ 0.0 $ 11.2 $ 0.0
French airport security services company          
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]          
Disposal Date Jun. 01, 2018        
Percent of shares sold 100.00%        
Net sales price $ 19.0        
Gain on sale of business   $ 11.2      
Annual revenues         $ 79.0