Fair Value Measurements (Financial Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Thousands		Mar. 31, 2022	Dec. 31, 2021
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Financial Assets		$ 370,872	$ 327,663
Total Financial Liabilities		1,801	4,291
Nuclear Decommissioning Trust [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Financial Assets	[1]	82,270	89,227
Nuclear Decommissioning Trust - Net Asset Value [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Financial Assets	[1],[2]	174,590	187,431
Unrestricted Investment And Other [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Financial Assets	[3]	232	212
Derivatives - Gas And Power [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Financial Assets	[4]	113,780	50,793
Total Financial Liabilities	[4]	1,801	4,291
Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Financial Assets		176,563	121,305
Quoted Prices In Active Markets For Identical Assets (Level 1) [Member] | Nuclear Decommissioning Trust [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Financial Assets	[1]	82,270	89,227
Quoted Prices In Active Markets For Identical Assets (Level 1) [Member] | Nuclear Decommissioning Trust - Net Asset Value [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Financial Assets	[1],[2]	0	0
Quoted Prices In Active Markets For Identical Assets (Level 1) [Member] | Unrestricted Investment And Other [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Financial Assets	[3]	0	0
Quoted Prices In Active Markets For Identical Assets (Level 1) [Member] | Derivatives - Gas And Power [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Financial Assets	[4]	94,293	32,078
Significant Other Observable Inputs (Level 2) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Financial Assets		11,245	3,917
Total Financial Liabilities		1,801	4,291
Significant Other Observable Inputs (Level 2) [Member] | Nuclear Decommissioning Trust [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Financial Assets	[1]	0	0
Significant Other Observable Inputs (Level 2) [Member] | Nuclear Decommissioning Trust - Net Asset Value [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Financial Assets	[1],[2]	0	0
Significant Other Observable Inputs (Level 2) [Member] | Unrestricted Investment And Other [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Financial Assets	[3]	232	212
Significant Other Observable Inputs (Level 2) [Member] | Derivatives - Gas And Power [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Financial Assets	[4]	11,013	3,705
Total Financial Liabilities	[4]	1,801	4,291
Significant Unobservable Inputs (Level 3)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Financial Assets		8,474	15,010
Significant Unobservable Inputs (Level 3) | Derivatives - Gas And Power [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Financial Assets	[4]	$ 8,474	$ 15,010

[1] For additional information about our nuclear decommissioning trust, see Note 4—Investments below.

[2] Nuclear decommissioning trust includes investments measured at net asset value per share (or its equivalent) as a practical expedient and these investments have not been categorized in the fair value hierarchy.  The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in our Condensed Consolidated Balance Sheet.

[3] Unrestricted investments and other includes investments that are related to equity securities.

[4] Derivatives - gas and power represent natural gas futures contracts (Level 1 and Level 2) and financial transmission rights (Level 3).  Level 1 are indexed against NYMEX.  Level 2 are valued by ACES using observable market inputs for similar transactions.  Level 3 are valued by ACES using unobservable market inputs, including situations where there is little market activity.  Sensitivity in the market price of financial transmission rights could impact the fair value.  For additional information about our derivative financial instruments, see Note 1 of the Notes to Consolidated Financial Statements in our 2021 Annual Report on Form 10-K.