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Revenue Recognition - Narrative (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2019
Sep. 30, 2018
Sep. 30, 2019
Sep. 30, 2018
Dec. 31, 2018
UNITED STATES          
Concentration Risk [Line Items]          
Concentration Risk, Percentage 90.00% 89.60% 89.50% 88.70%  
Topic 606          
Concentration Risk [Line Items]          
Accounts receivable $ 16.3   $ 16.3   $ 19.5