Carrying value as of the balance sheet date of long-term debt (with maturities initially due after one year or beyond the operating cycle if longer) identified as Convertible Notes Payable, excluding current portion. Convertible Notes Payable is a written promise to pay a note which can be exchanged for a specified amount of another, related security, at the option of the issuer and the holder.

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Debt - Senior Convertible Notes (Details) - USD ($)	6 Months Ended	12 Months Ended
Debt - Senior Convertible Notes (Details) - USD ($)	Jun. 30, 2020	Dec. 31, 2019	May 31, 2020	Nov. 30, 2018	Jun. 30, 2017
Debt Instrument [Line Items]
Carrying amount of liability component	$ 1,658,800,000	$ 1,059,700,000
Senior Notes
Debt Instrument [Line Items]
Principal amount	2,094,700,000	1,250,000,000.0
Unamortized debt discount	(414,200,000)	(177,200,000)
Unamortized debt issuance costs	(21,700,000)	(13,100,000)
Carrying amount of liability component	1,658,800,000	1,059,700,000
Carrying amount of equity component	467,700,000	242,200,000
Senior Notes \| Senior Convertible Notes due 2022
Debt Instrument [Line Items]
Principal amount	37,200,000	$ 400,000,000.0	$ 260,000,000.0		$ 400,000,000.0
Unamortized debt discount	(2,800,000)
Unamortized debt issuance costs	$ (300,000)
Remaining amortization period of debt discount on the liability component	1 year 10 months 24 days	2 years 6 months
Senior Notes \| Senior Convertible Notes due 2023
Debt Instrument [Line Items]
Principal amount	$ 850,000,000.0	$ 850,000,000.0		$ 850,000,000.0
Remaining amortization period of debt discount on the liability component	3 years 4 months 24 days	4 years
Senior Notes \| Senior Convertible Notes due 2025
Debt Instrument [Line Items]
Principal amount	$ 1,207,500,000	$ 0	$ 1,210,000,000
Remaining amortization period of debt discount on the liability component	5 years 4 months 24 days