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Cash, Cash Equivalents and Short-Term Investments - Narrative (Details)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2020
USD ($)
investment_type
investment
Sep. 30, 2019
USD ($)
Sep. 30, 2020
USD ($)
investment_type
investment
Sep. 30, 2019
USD ($)
Dec. 31, 2019
USD ($)
Investment Holdings [Line Items]          
Cash in transit for credit and debit card transactions $ 12.2   $ 12.2   $ 11.5
Number of investments in unrealized loss positions | investment 55   55    
Number of security types | investment_type 8   8    
Number of security types in loss position | investment_type 1   1    
Investment income $ 2.6 $ 5.7 $ 10.4 $ 17.5  
Corporate notes and obligations          
Investment Holdings [Line Items]          
Unrealized losses, short term investments $ 0.1   $ 0.1