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Discontinued operations - Narrative (Details) $ in Thousands |  |  |  | 3 Months Ended | 6 Months Ended |
--- | --- | --- | --- | --- | --- | ---
May 31, 2024 shares | May 31, 2023 shares | Apr. 25, 2023 USD ($) | Jun. 30, 2024 USD ($) | Jun. 30, 2023 USD ($) | Jun. 30, 2024 USD ($) | Jun. 30, 2023 USD ($) | Dec. 31, 2023 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |
Long-term debt |  |  |  | $ 2,400,617 | $ 2,247,422 | $ 2,400,617 | $ 2,247,422 | $ 2,298,223
Repayment of long-term debt |  |  |  |  |  | 11,127 | 506,191 |
Treasury stock retired (in shares) | shares | 538,921 |  |  |  |  |  |  |
Separation related costs |  |  |  | 138 | 41,200 | 138 | 46,100 |
Discontinued Operations, Disposed of by Means Other than Sale, Spinoff | Knife River Corporation |  |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |
Pro rata distribution of shares, percentage |  | 0.90 |  |  |  |  |  |
Stock split, conversion ratio |  | 4 |  |  |  |  |  |
Retained ownership percentage |  | 0.10 |  |  |  |  |  |
Number of retained shares (in shares) | shares |  | 5,700,000 |  |  |  |  |  |
Discontinued Operations, Disposed of by Means Other than Sale, Spinoff | Knife River Corporation | Cash Received, TSA |  |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |
Discontinued operation, amount of continuing cash flows after disposal |  |  |  | 437 | 599 | 1,500 | 599 |
Discontinued Operations, Disposed of by Means Other than Sale, Spinoff | Knife River Corporation | Cash Paid, TSA |  |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |
Discontinued operation, amount of continuing cash flows after disposal |  |  |  | $ 62 | $ 277 | $ 140 | $ 277 |
Knife River Corporation |  |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |
Repayment of long-term debt |  |  | $ 825,000 |  |  |  |  |
Knife River Corporation | Revolving Credit Facility |  |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity |  |  | 350,000 |  |  |  |  |
Knife River Corporation | Term Loan Agreement |  |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |
Debt instrument, face amount |  |  | 275,000 |  |  |  |  |
Senior Notes | Knife River Corporation |  |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |
Long-term debt |  |  | $ 425,000 |  |  |  |  |

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