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Notes Payable - Issuance (Details) - USD ($)
1 Months Ended
May 31, 2018
Mar. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Convertible senior notes, 0.25%, due 2023        
Debt Instrument [Line Items]        
Aggregate principal amount   $ 549,998,000 $ 549,999,000 $ 550,000,000.0
Interest rate (as a percent) 0.25%      
Net proceeds from the debt offering $ 537,000,000.0      
Convertible senior notes, 0.25%, due 2023 - over-allotment        
Debt Instrument [Line Items]        
Aggregate principal amount $ 75,000,000.0