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Fair value - other postretirement (Details 9) - Other Postretirement Benefits - Qualified Plan - Overfunded Plan - USD ($) $ in Thousands | Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020
--- | --- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of net plan assets at end of year | $ 76,326 | $ 100,158 | $ 101,639
Defined Benefit Plan, Cash and Cash Equivalents [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount | $ 4,196 | 4,281 |
Postretirement Investments in Collective and Mutual Funds | 7.00% |  |
Defined Benefit Plan, Equity Securities, US [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount | $ 2,572 | 2,332 |
Defined Benefit Plan, Equity Securities, Non-US [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount |  | $ 1 |
Postretirement Investments in Collective and Mutual Funds | 16.00% | 19.00% |
Collective and mutual funds [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount | $ 10 | $ 94 |
Insurance investment contract [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount | 69,548 | 93,447 |
Total assets measured at fair value [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of net plan assets at end of year | $ 76,326 | $ 100,158 |
Corporate debt securities [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Postretirement Investments in Collective and Mutual Funds | 29.00% | 37.00% |
Postretirement Investments in Insurance Contracts | 69.00% | 58.00% |
Defined Benefit Plan, Equity Securities, US, Large Cap [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Postretirement Investments in Collective and Mutual Funds | 24.00% | 16.00% |
Postretirement Investments in Insurance Contracts | 14.00% | 13.00% |
Defined Benefit Plan, Equity Securities, US, Small Cap [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Postretirement Investments in Insurance Contracts | 4.00% | 5.00% |
U.S. Government securities [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Postretirement Investments in Collective and Mutual Funds | 7.00% | 9.00% |
Postretirement Investments in Insurance Contracts | 13.00% | 13.00% |
Other Investments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Postretirement Investments in Collective and Mutual Funds | 17.00% | 19.00% |
Postretirement Investments in Insurance Contracts |  | 11.00% |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Defined Benefit Plan, Equity Securities, US [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount | $ 2,572 | $ 2,332 |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Collective and mutual funds [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount | 5 | 4 |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Total assets measured at fair value [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of net plan assets at end of year | 2,577 | 2,336 |
Significant Other Observable Inputs (Level 2) | Defined Benefit Plan, Cash and Cash Equivalents [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount | 4,196 | 4,281 |
Significant Other Observable Inputs (Level 2) | Defined Benefit Plan, Equity Securities, Non-US [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount |  | 1 |
Significant Other Observable Inputs (Level 2) | Collective and mutual funds [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount | 5 | 90 |
Significant Other Observable Inputs (Level 2) | Insurance investment contract [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount | 69,548 | 93,447 |
Significant Other Observable Inputs (Level 2) | Total assets measured at fair value [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of net plan assets at end of year | $ 73,749 | 97,819 |
Fair Value Measured at Net Asset Value Per Share | Collective and mutual funds [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount |  | $ 3 |

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