Financial Instruments And Investments (Carrying Amount and Fair Value Amounts) (Details) - USD ($) $ in Thousands		Sep. 30, 2019	Dec. 31, 2018
Carrying (Reported) Amount, Fair Value Disclosure
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure		$ 1,485,617	$ 1,434,426
Carrying (Reported) Amount, Fair Value Disclosure | Pollution Control Bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure	[1]	157,947	157,769
Carrying (Reported) Amount, Fair Value Disclosure | Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure		1,118,255	1,117,943
Carrying (Reported) Amount, Fair Value Disclosure | RGRT Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure	[2]	109,589	109,507
Carrying (Reported) Amount, Fair Value Disclosure | Revolving Credit Facility
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure	[2]	99,826	49,207
Estimate of Fair Value Measurement
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure		1,776,378	1,566,874
Estimate of Fair Value Measurement | Pollution Control Bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure	[1]	167,977	161,917
Estimate of Fair Value Measurement | Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure		1,393,650	1,244,310
Estimate of Fair Value Measurement | RGRT Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure	[2]	114,925	111,440
Estimate of Fair Value Measurement | Revolving Credit Facility
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure	[2]	$ 99,826	$ 49,207

[1] On February 1, 2019 and April 1, 2019, the Company purchased in lieu of redemption the 2009 Series A 7.25% PCBs with an aggregate principal amount of $63.5 million and the 2009 Series B 7.25% PCBs with an aggregate principal amount of $37.1 million, respectively, utilizing funds borrowed under the RCF. On May 22, 2019, the Company reoffered and sold $63.5 million aggregate principal amount of 2009 Series A 7.25% PCBs and $37.1 million aggregate principal amount of 2009 Series B 7.25% PCBs with a fixed interest rate of 3.60% per annum until the bonds mature on February 1, 2040 and April 1, 2040, respectively. See Part I, Item 1, Financial Statements, Note M of Notes to Financial Statements for further discussion.

[2] Nuclear fuel financing, as of September 30, 2019 and December 31, 2018, is funded through $110 million RGRT Senior Notes and $22.8 million and $26.2 million, respectively, under the RCF. As of September 30, 2019, $77.0 million was outstanding under the RCF for working capital and general corporate purposes. As of December 31, 2018, $23.0 million, was outstanding under the RCF for working capital or general corporate purposes. The interest rate on the Company's borrowings under the RCF is reset throughout the quarter reflecting current market rates. Consequently, the carrying value approximates fair value. See Part I, Item 1, Financial Statements, Note M of Notes to Financial Statements for further discussion.