Estimated future benefit payments and subsidies (Details 7) - Qualified Plan - USD ($)	12 Months Ended
Dec. 31, 2020	Dec. 31, 2021
Underfunded Plan \| Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year		$ 0
Defined Benefit Plan, Plan Assets, Additional Contributions by Employer	$ 20,000,000
2022		24,644,000
2023		24,766,000
2024		24,897,000
2025		24,739,000
2026		24,571,000
2027-2031		117,413,000
Overfunded Plan \| Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year		601,000
2022		4,393,000
2023		4,522,000
2024		4,572,000
2025		4,612,000
2026		4,642,000
2027-2031		17,867,000
2022		70,000
2023		65,000
2024		58,000
2025		52,000
2026		46,000
2027-2031		$ 157,000

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Amount of contribution expected to be received by defined benefit plan from employer in next fiscal year following current fiscal year.

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