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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Remaining amortization period for discount on the liability component of convertible debt which may be settled in cash upon conversion, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Face (par) amount of debt instrument at time of issuance.

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The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

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Debt - Senior Convertible Notes (Details) - USD ($)	12 Months Ended
Debt - Senior Convertible Notes (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2019	May 31, 2020	Nov. 30, 2018	Jun. 12, 2017
Senior Convertible Notes
Carrying amount of liability component	$ 1,667,200,000	$ 1,059,700,000
Senior Notes
Senior Convertible Notes
Total principal amount	2,057,500,000	1,250,000,000.0
Unamortized debt discount	(371,100,000)	(177,200,000)
Unamortized debt issuance costs	(19,200,000)	(13,100,000)
Carrying amount of liability component	1,667,200,000	1,059,700,000
Carrying value of equity component	461,000,000.0	242,200,000
Senior Notes \| Convertible Notes due 2022
Senior Convertible Notes
Total principal amount	0	$ 400,000,000.0	$ 260,000,000.0		$ 400,000,000.0
Remaining amortization period of debt discount on the liability component:		2 years 6 months
Senior Notes \| Convertible Notes due 2023
Senior Convertible Notes
Total principal amount	$ 850,000,000.0	$ 850,000,000.0		$ 850,000,000.0
Remaining amortization period of debt discount on the liability component:	2 years 10 months 24 days	4 years
Senior Notes \| Convertible Notes due 2025
Senior Convertible Notes
Total principal amount	$ 1,207,500,000	$ 0	$ 1,210,000,000
Remaining amortization period of debt discount on the liability component:	4 years 10 months 24 days