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Other Comprehensive Income: Reclassification Out of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2021 | Jun. 30, 2021 | Mar. 31, 2021 | Sep. 30, 2020 | Jun. 30, 2020 | Mar. 31, 2020 | Sep. 30, 2021 | Sep. 30, 2020
Condensed Statement of Income Captions [Line Items] |  |  |  |  |  |  |  |
Interest Expense | $ 38,604 |  |  | $ 36,521 |  |  | $ 115,098 | $ 108,067
Fuel, purchased power and cost of natural gas sold | 94,057 |  |  | 71,686 |  |  | 495,678 | 331,194
Operations and maintenance | 122,277 |  |  | 122,759 |  |  | 375,201 | 365,533
Income tax benefit (expense) | (5,253) |  |  | (4,651) |  |  | (6,333) | (25,484)
Net income (loss) | 48,162 | $ 28,287 | $ 100,487 | 40,349 | $ 24,694 | $ 97,224 | 176,936 | 162,267
Reclassification out of Accumulated Other Comprehensive Income |  |  |  |  |  |  |  |
Condensed Statement of Income Captions [Line Items] |  |  |  |  |  |  |  |
Net income (loss) | (847) |  |  | (1,111) |  |  | (2,701) | (3,497)
Reclassification out of Accumulated Other Comprehensive Income | Cash Flow Hedging |  |  |  |  |  |  |  |
Condensed Statement of Income Captions [Line Items] |  |  |  |  |  |  |  |
Income before Income Taxes | (381) |  |  | (890) |  |  | (1,782) | (2,872)
Income tax benefit (expense) | (26) |  |  | 209 |  |  | 308 | 680
Net income (loss) | (407) |  |  | (681) |  |  | (1,474) | (2,192)
Reclassification out of Accumulated Other Comprehensive Income | Cash Flow Hedging | Interest rate swaps |  |  |  |  |  |  |  |
Condensed Statement of Income Captions [Line Items] |  |  |  |  |  |  |  |
Interest Expense | (712) |  |  | (712) |  |  | (2,138) | (2,138)
Reclassification out of Accumulated Other Comprehensive Income | Cash Flow Hedging | Commodity Contract |  |  |  |  |  |  |  |
Condensed Statement of Income Captions [Line Items] |  |  |  |  |  |  |  |
Fuel, purchased power and cost of natural gas sold | 331 |  |  | (178) |  |  | 356 | (734)
Reclassification out of Accumulated Other Comprehensive Income | Accumulated Defined Benefit Plans Adjustment, Net Prior Service Cost |  |  |  |  |  |  |  |
Condensed Statement of Income Captions [Line Items] |  |  |  |  |  |  |  |
Operations and maintenance | 25 |  |  | 24 |  |  | 74 | 79
Reclassification out of Accumulated Other Comprehensive Income | Accumulated Defined Benefit Plans Adjustment, Net Unamortized Gain (Loss) |  |  |  |  |  |  |  |
Condensed Statement of Income Captions [Line Items] |  |  |  |  |  |  |  |
Operations and maintenance | (598) |  |  | (597) |  |  | (1,793) | (1,791)
Reclassification out of Accumulated Other Comprehensive Income | Accumulated Defined Benefit Plans Adjustment |  |  |  |  |  |  |  |
Condensed Statement of Income Captions [Line Items] |  |  |  |  |  |  |  |
Income before Income Taxes | (573) |  |  | (573) |  |  | (1,719) | (1,712)
Income tax benefit (expense) | 133 |  |  | 143 |  |  | 492 | 407
Net income (loss) | $ (440) |  |  | $ (430) |  |  | $ (1,227) | $ (1,305)

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