Financial Instruments And Investments (Carrying Amount and Fair Value Amounts) (Details) - USD ($) $ in Thousands		Mar. 31, 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		$ 1,525,612	$ 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]	95,088	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		1,118,036	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]	109,537	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]	202,951	49,207
Estimate of Fair Value Measurement
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure		1,697,218	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]	98,217	161,917
Estimate of Fair Value Measurement | Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure		1,283,200	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]	112,850	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]	$ 202,951	$ 49,207

[1] On February 1, 2019, the Company purchased in lieu of redemption all of the 2009 Series A 7.25% PCBs with a principal amount of $63.5 million, utilizing funds borrowed under the RCF. The Company is currently holding the 2009 Series A 7.25% PCBs and may remarket them or replace them with debt instruments of equivalent value at a future date depending on the Company's financing needs and market conditions, and in accordance with the Company's regulators' approvals. See Part I, Item 1, Financial Statements, Note M of Notes to Financial Statements for further discussion.

[2] Nuclear fuel financing, as of March 31, 2019 and December 31, 2018, is funded through $110 million RGRT Senior Notes and $30.0 million and $26.2 million, respectively, under the RCF. As of March 31, 2019, $173.0 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.