Fair value - pension (Details 8) - Qualified Plan - Underfunded Plan - Pension Benefits - 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	$ 373,109	$ 383,834	$ 365,264
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	$ 4,637	$ 7,841
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Percentage		8.00%
Pension investments in insurance contracts	100.00%
Defined Benefit Plan, Equity Securities, US [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	$ 7,483	$ 12,844
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	$ 1,279	$ 1,727
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Percentage	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	$ 208,476	$ 233,185
Corporate debt securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	$ 125,167	$ 92,809
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Percentage	37.00%	36.00%
Municipal bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	$ 7,507	$ 10,126
U.S. Government securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	$ 9,015	$ 13,872
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Percentage	9.00%	5.00%
Pooled Separate Accounts
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	$ 3,088
Total assets measured at fair value [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of net plan assets at end of year	$ 373,109	$ 383,834
Defined Benefit Plan, Equity Securities, US, Large Cap [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Percentage	16.00%	18.00%
Other Investments
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Percentage	19.00%	9.00%
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	$ 7,483	$ 12,844
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	167,093	177,397
Quoted Prices in Active Markets for Identical Assets  (Level 1) | U.S. Government securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	7,113	11,177
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	181,689	201,418
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	4,637	7,841
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	1,279	1,727
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	41,383	55,788
Significant Other Observable Inputs  (Level 2) | Corporate debt securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	125,167	92,809
Significant Other Observable Inputs  (Level 2) | Municipal bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	7,507	10,126
Significant Other Observable Inputs  (Level 2) | U.S. Government securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	1,902	2,695
Significant Other Observable Inputs  (Level 2) | Pooled Separate Accounts
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	3,088
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	184,963	170,986
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	$ 6,457	$ 11,430