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Fair value - other postretirement (Details 9) - Other Postretirement Benefits - Qualified Plan - Overfunded Plan - USD ($) $ in Thousands | Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of net plan assets at end of year | $ 100,158 | $ 101,639 | $ 94,587
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 | 4,281 | $ 3,517 |
Postretirement Investments in Collective and Mutual Funds |  | 8.00% |
Postretirement Investments in Insurance Contracts |  | 1.00% |
Defined Benefit Plan, Equity Securities, US [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount | 2,332 | $ 1,850 |
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 | $ 2 |
Postretirement Investments in Collective and Mutual Funds | 19.00% | 24.00% |
Collective and mutual funds [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount | $ 94 | $ 157 |
Insurance investment contract [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount | 93,447 | 96,103 |
Total assets measured at fair value [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of net plan assets at end of year | $ 100,158 | $ 101,639 |
Corporate debt securities [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Postretirement Investments in Collective and Mutual Funds | 37.00% | 36.00% |
Postretirement Investments in Insurance Contracts | 58.00% | 67.00% |
Defined Benefit Plan, Equity Securities, US, Large Cap [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Postretirement Investments in Collective and Mutual Funds | 16.00% | 18.00% |
Postretirement Investments in Insurance Contracts | 13.00% | 10.00% |
Defined Benefit Plan, Equity Securities, US, Small Cap [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Postretirement Investments in Insurance Contracts | 5.00% | 4.00% |
U.S. Government securities [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Postretirement Investments in Collective and Mutual Funds | 9.00% | 5.00% |
Postretirement Investments in Insurance Contracts | 13.00% | 12.00% |
Other Investments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Postretirement Investments in Collective and Mutual Funds | 19.00% | 9.00% |
Postretirement Investments in Insurance Contracts | 11.00% | 6.00% |
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 | $ 2,332 | $ 1,850 |
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 | 4 | 10 |
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 | 2,336 | 1,860 |
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 | 4,281 | 3,517 |
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 | 2 |
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 | 90 | 147 |
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 | 93,447 | 96,103 |
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 | 97,819 | 99,769 |
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 | $ 10 |

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