Estimated future benefit payments and subsidies (Details 8) - Qualified Plan	12 Months Ended
Dec. 31, 2019 USD ($)
Underfunded Plan \| Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Additional Contributions by Employer	$ 20,000,000.0
2020	24,128,000
2021	24,432,000
2022	24,642,000
2023	24,874,000
2024	24,924,000
2025-2029	121,205,000
Overfunded Plan \| Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year	660,000
2020	5,024,000
2020	92,000
2021	5,073,000
2021	86,000
2022	5,098,000
2022	80,000
2023	5,091,000
2023	73,000
2024	5,000,000
2024	65,000
2025-2029	24,242,000
2025-2029	$ 222,000

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