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Postretirement Benefit Plans (Assumptions Used) (Details) | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Defined Benefit Postretirement Health And Life Coverage [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, assumptions used calculating benefit obligation, Discount rate | 2.25% | 3.00% |
Defined benefit plan, assumptions used calculating benefit obligation, Rate of compensation increase | 2.00% | 2.00% |
Defined benefit plan, assumptions used calculating net periodic benefit cost, Discount rate | 3.00% | 4.00% | 3.50%
Defined benefit plan, assumptions used calculating net periodic benefit cost, Rate of compensation increase | 2.00% | 3.00% | 2.50%
Director's Retirement Plan [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, assumptions used calculating benefit obligation, Discount rate | 2.25% | 3.00% |
Defined benefit plan, assumptions used calculating net periodic benefit cost, Discount rate | 2.25% | 3.00% | 4.00%
Defined benefit plan, assumptions used calculating benefit obligation, Change in consumer price index | 1.00% | 1.00% |
Defined benefit plan, assumptions used calculating net periodic benefit cost, Changes in consumer price index | 1.00% | 1.00% | 2.00%
Scottdale Defined Benefit Pension Plan [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, assumptions used calculating benefit obligation, Discount rate | 2.50% | 3.25% |
Defined benefit plan, assumptions used calculating benefit obligation, Rate of compensation increase | 2.50% | 3.00% |
Defined benefit plan, assumptions used calculating benefit obligation, Expected long-term return on plan assets | 4.50% | 5.00% |

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- Definition Percentage change in the Consumer Price Index, which is measure that examines the weighted average of prices of a basket of consumer goods and services + References No definition available. + Details
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- Definition Percentage change in the Consumer Price Index, which is measure that examines the weighted average of prices of a basket of consumer goods and services + References No definition available. + Details
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- Definition Weighted average rate for present value of future retirement benefits cash flows, used to determine benefit obligation of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(1) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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- Definition Weighted average rate increase of compensation, used to determine benefit obligation of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(2) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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- Definition Weighted average rate for present value of future retirement benefits cash flows, used to determine net periodic benefit cost of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(1) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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- Definition Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(3) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e2919-114920 + Details
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- Definition Weighted average rate of compensation increase used to determine net periodic benefit cost of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(2) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Details
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- Details
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