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Other Comprehensive Income: Reclassification Out of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands | 3 Months Ended
--- | ---
Mar. 31, 2021 | Mar. 31, 2020
Condensed Statement of Income Captions [Line Items] |  |
Interest Expense | $ 37,825 | $ 35,781
Fuel, purchased power and cost of natural gas sold | 293,147 | 187,879
Operations and maintenance | 129,679 | 125,466
Income before Income Taxes | 100,981 | 113,226
Income tax benefit (expense) | (494) | (16,002)
Net income (loss) | 100,487 | 97,224
Reclassification out of Accumulated Other Comprehensive Income |  |
Condensed Statement of Income Captions [Line Items] |  |
Net income (loss) | (911) | (1,393)
Cash Flow Hedging | Reclassification out of Accumulated Other Comprehensive Income |  |
Condensed Statement of Income Captions [Line Items] |  |
Income before Income Taxes | (744) | (1,199)
Income tax benefit (expense) | 198 | 285
Net income (loss) | (546) | (914)
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Cost | Reclassification out of Accumulated Other Comprehensive Income |  |
Condensed Statement of Income Captions [Line Items] |  |
Operations and maintenance | 25 | 30
Accumulated Defined Benefit Plans Adjustment, Net Unamortized Gain (Loss) | Reclassification out of Accumulated Other Comprehensive Income |  |
Condensed Statement of Income Captions [Line Items] |  |
Operations and maintenance | (598) | (597)
Accumulated Defined Benefit Plans Adjustment | Reclassification out of Accumulated Other Comprehensive Income |  |
Condensed Statement of Income Captions [Line Items] |  |
Income before Income Taxes | (573) | (567)
Income tax benefit (expense) | 208 | 88
Net income (loss) | (365) | (479)
Interest rate swaps | Cash Flow Hedging | Reclassification out of Accumulated Other Comprehensive Income |  |
Condensed Statement of Income Captions [Line Items] |  |
Interest Expense | (713) | (713)
Commodity Contract | Cash Flow Hedging | Reclassification out of Accumulated Other Comprehensive Income |  |
Condensed Statement of Income Captions [Line Items] |  |
Fuel, purchased power and cost of natural gas sold | $ (31) | $ (486)

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- Definition Amount of income (loss) from continuing operations before deduction of income tax expense (benefit) and income (loss) attributable to noncontrolling interest, and addition of income (loss) from equity method investments. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 32 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8933-108599 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 32 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8933-108599 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 30 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8906-108599 Reference 4: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 31 -URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8924-108599 Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08.(h)(1)(i)) -URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 22 -URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8736-108599 + Details
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