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Estimated future benefit payments and subsidies (Details 8) - Qualified Plan | 12 Months Ended
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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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