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Postretirement Benefit Plans (Weighted-Average Asset Allocation By Investment Category) (Details) - Scottdale Defined Benefit Pension Plan [Member] | Dec. 31, 2020 | Dec. 31, 2019
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Defined Benefit Plan Disclosure [Line Items] |  |
Defined benefit plan, Weighted-average asset allocation percent | 100.00% | 100.00%
Cash and Cash Equivalents [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined benefit plan, Weighted-average asset allocation percent | 10.57% | 51.76%
Common Stock [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined benefit plan, Weighted-average asset allocation percent | 58.45% | 35.23%
Corporate Bonds [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined benefit plan, Weighted-average asset allocation percent | 30.98% | 13.01%

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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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- Definition Percentage of actual investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(i) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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