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Senior Notes (Schedule Of Interest Expense Incurred In Connection With Senior Notes) (Details) - Senior Notes [Member] - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2021
Mar. 31, 2020
4.868% Senior notes due 6/1/2044 [Member]    
Debt Instrument [Line Items]    
Interest expense incurred $ 4,868 $ 4,868
Debt instrument, stated interest rate 4.868%  
3.5% Senior notes due 10/15/2050 [Member]    
Debt Instrument [Line Items]    
Interest expense incurred $ 8,805
Debt instrument, stated interest rate 3.50%