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Fair Value Measurements - Additional Information (Details) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2020
Jan. 01, 2020
Mar. 31, 2019
Fair Value Disclosures [Line Items]      
Available-for-sale Securities, Gross Unrealized Loss $ 0.9    
Fair value of convertible senior notes 912.1    
Domestic Cash and Investments      
Fair Value Disclosures [Line Items]      
Cash, cash equivalents and restricted cash $ 977.3   $ 963.4
Minimum      
Fair Value Disclosures [Line Items]      
Long-term investments maturity period 1 year    
Maximum      
Fair Value Disclosures [Line Items]      
Long-term investments maturity period 2 years    
Accumulated Other Comprehensive Gain (Loss)      
Fair Value Disclosures [Line Items]      
Debt Securities, Available-for-sale, Unrealized Loss $ 0.8    
Comprehensive Income      
Fair Value Disclosures [Line Items]      
Gross unrealized losses, no intent to sell $ 0.1    
Cumulative effect of adoption of ASC 326 | Accumulated Other Comprehensive Gain (Loss)      
Fair Value Disclosures [Line Items]      
Gross unrealized losses   $ 0.1