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