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Discontinued operations - Schedule of Income and Expense Constituting Pretax Income (Loss) From Discontinued Operations (Details) - Knife River Corporation - Discontinued Operations, Disposed of by Means Other than Sale, Spinoff - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended
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Jun. 30, 2024 | Jun. 30, 2023 | Jun. 30, 2024 | Jun. 30, 2023
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |
Operating revenues | $ 0 | $ 428,020 | $ 0 | $ 735,259
Operating expenses | 161 | 416,686 | 161 | 767,960
Operating (loss) income | (161) | 11,334 | (161) | (32,701)
Other income | 0 | 1,889 | 0 | 2,381
Interest expense | 0 | 23,544 | 0 | 37,611
Loss from discontinued operations before income taxes | (161) | (10,321) | (161) | (67,931)
Income tax (benefit) expense | (23) | 6,620 | (23) | (5,467)
Discontinued operations, net of tax | $ (138) | $ (16,941) | $ (138) | $ (62,464)

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- Definition Amount before tax of income (loss) from a discontinued operation. Includes, but is not limited to, the income (loss) from operations during the phase-out period, gain (loss) on disposal, gain (loss) for reversal of write-down (write-down) to fair value, less cost to sell, and adjustments to a prior period gain (loss) on disposal. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 944 -SubTopic 220 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04(12)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147477250/944-220-S99-1 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 205 -SubTopic 20 -Name Accounting Standards Codification -Section 45 -Paragraph 3A -Publisher FASB -URI https://asc.fasb.org/1943274/2147483475/205-20-45-3A Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 205 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 5B -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147483499/205-20-50-5B Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 205 -SubTopic 20 -Name Accounting Standards Codification -Section 45 -Paragraph 3B -Publisher FASB -URI https://asc.fasb.org/1943274/2147483475/205-20-45-3B Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 205 -SubTopic 20 -Name Accounting Standards Codification -Section 45 -Paragraph 4 -Publisher FASB -URI https://asc.fasb.org/1943274/2147483475/205-20-45-4 Reference 6: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 205 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147483499/205-20-50-1 Reference 7: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 205 -SubTopic 20 -Name Accounting Standards Codification -Section 45 -Paragraph 3 -Publisher FASB -URI https://asc.fasb.org/1943274/2147483475/205-20-45-3 Reference 8: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 220 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03(14)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147483621/220-10-S99-2 + Details
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