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Post Retirement Benefits (Details) - USD ($) | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2010
Amounts that will be amortized from accumulated other comprehensive income in next fiscal year: |  |  |  |  |
Interest cost |  | $ 285,000 | $ 277,000 | $ 298,000 |
Postretirement benefits |  |  |  |  |
Postretirement benefits: |  |  |  |  |
Decrease in post retirement obligations |  |  |  |  | $ 10,282,000
Amortization period |  |  |  |  | 20 years
Change in net periodic benefit cost due to plan amendment |  | 496,000 | 496,000 | $ 496,000 |
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss) |  | 1,099,000 | 910,000 |  |
Amounts that will be amortized from accumulated other comprehensive income in next fiscal year: |  |  |  |  |
Interest cost |  | $ 285,000 | $ 277,000 |  |
Assumed health care cost trend rates: |  |  |  |  |
Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Next Fiscal Year |  | 6.00% | 6.20% |  |
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate |  | 5.00% | 5.00% |  |
Effect of changing the health care cost trend rate by one-percentage point for each future year: |  |  |  |  |
Effect on total of service and interest cost components, 1 - percentage point increase |  | $ 39,000 |  |  |
Effect on total of service and interest cost components, 1 - percentage point decrease |  | (33,000) |  |  |
Effect on post retirement benefit obligation, 1 - percentage point increase |  | 1,169,000 |  |  |
Effect on post retirement benefit obligation, 1 - percentage point decrease |  | $ (997,000) |  |  |
Scenario, Forecast [Member] | Postretirement benefits |  |  |  |  |
Postretirement benefits: |  |  |  |  |
Change in net periodic benefit cost due to plan amendment | $ 496,000 |  |  |  |
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss) | (78,000) |  |  |  |
Amounts that will be amortized from accumulated other comprehensive income in next fiscal year: |  |  |  |  |
Amortization of prior service credit, net of tax | (496,000) |  |  |  |
Amortization of loss, net of tax | (181,000) |  |  |  |
Interest cost | $ 237,000 |  |  |  |

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- Definition Amount of gain (loss) from change in actuarial assumptions which (increases) decreases benefit obligation of defined benefit plan. Assumptions include, but are not limited to, interest, mortality, employee turnover, salary, and temporary deviation from substantive plan. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(4) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 + Details
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- Definition Assumed rate, for next fiscal year, based on annual change in cost of health care cost benefits used to measure expected cost of benefits covered by defined benefit postretirement plan. Factors include, but are not limited to, estimate of health care inflation, change in health care utilization or delivery pattern, technological advances, and change in health status of participant. Excludes factors for change in composition of plan population by age and dependency status. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (l) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 + Details
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