Long-term Debt (Schedule Of Long-term Debt) (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Debt Instrument [Line Items]
Long-term debt	$ 976,955	$ 1,025,996
Debt issuance costs	(4,369)	(4,788)
Current maturities	(49,041)	(49,041)
Long-term debt, excluding current maturities	923,545	972,167
$250,000,000 principal amount of First Mortgage Bonds, 2017 Series A due 2037 at an interest rate of 3.33%
Debt Instrument [Line Items]
Long-term debt	175,000	187,500
$260,000,000 principal amount of First Mortgage Bonds, 2015 Series A due 2044 at an interest rate of 4.46%
Debt Instrument [Line Items]
Long-term debt	260,000	260,000
$72,000,000 principal amount of First Mortgage Bonds, 2015 Series B due 2053 at an interest rate of 4.56%
Debt Instrument [Line Items]
Long-term debt	72,000	72,000
$50,000,000 principal amount of First Mortgage Bonds, 2013 Series A due 2043 at an interest rate of 4.21%
Debt Instrument [Line Items]
Long-term debt	50,000	50,000
$50,000,000 principal amount of First Mortgage Bonds, 2013 Series B due 2053 at an interest rate of 4.36%
Debt Instrument [Line Items]
Long-term debt	50,000	50,000
$90,000,000 principal amount of First Mortgage Bonds, 2011 Series A due 2040 at an interest rate of 4.83%
Debt Instrument [Line Items]
Long-term debt	51,000	54,000
$165,000,000 principal amount of First Mortgage Bonds, 2011 Series B due 2040 at an interest rate of 5.54%
Debt Instrument [Line Items]
Long-term debt	140,250	148,500
$95,000,000 principal amount of First Mortgage Bonds, 2011 Series C due 2050 at an interest rate of 5.54%
Debt Instrument [Line Items]
Long-term debt	64,125	66,500
$250,000,000 principal amount of 2003 Series A Bonds due 2028 at an interest rate of 5.676%
Debt Instrument [Line Items]
Long-term debt	52,080	62,496
$300,000,000 principal amount of 2002 Series B Bonds due 2028 at an interest rate of 6.21%
Debt Instrument [Line Items]
Long-term debt	$ 62,500	$ 75,000