Debt And Interest Expense (Convertible Debentures) (Narrative) (Details) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	May 01, 2018
Debt Instrument [Line Items]
Loss on Extinguishment of Debt	$ 0	$ 0	$ 6,554
Principal amount of debt				$ 1,250,000
Stock Issued During Period, Shares, Conversion of Convertible Securities			26,100

Number of shares issued during the period as a result of the conversion of convertible securities.

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Name:	us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration