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Cash, Cash Equivalents and Short-Term Investments - Narrative (Details)
$ in Millions
3 Months Ended
Mar. 31, 2020
USD ($)
investment
investment_type
Mar. 31, 2019
USD ($)
Dec. 31, 2019
USD ($)
Cash and Cash Equivalents [Line Items]      
Cash in transit for credit and debit card transactions $ 11.8   $ 11.5
Short-term investments $ 614.4    
Number of investments in unrealized loss positions | investment 194    
Short-Term Investments, Number of Security Types | investment_type 9    
Short-Term Investments, Number of Security Types In Loss Position | investment_type 2    
Investment income $ (5.1) $ (6.2)  
Corporate notes and obligations      
Cash and Cash Equivalents [Line Items]      
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss 2.7    
Asset-backed securities      
Cash and Cash Equivalents [Line Items]      
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss $ 0.7