Employee Benefit Plans (Summary Of Current Allocation Percentages Of Plan Assets) (Details)	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Horizon Defined Benefit Plan
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	100.00%
Percentage of Plan Assets	100.00%	100.00%
Horizon Defined Benefit Plan \| Common stocks
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	60.00%
Percentage of Plan Assets	55.00%	48.00%
Horizon Defined Benefit Plan \| Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	20.00%
Percentage of Plan Assets	23.00%	25.00%
Horizon Defined Benefit Plan \| Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	5.00%
Percentage of Plan Assets	9.00%	15.00%
Horizon Defined Benefit Plan \| Alternative investments
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	15.00%
Percentage of Plan Assets	13.00%	12.00%
Horizon Defined Benefit Plan \| Minimum \| Common stocks
Defined Benefit Plan Disclosure [Line Items]
Allowable-Allocation Range, Minimum	0.35
Horizon Defined Benefit Plan \| Minimum \| Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Allowable-Allocation Range, Minimum	.1
Horizon Defined Benefit Plan \| Minimum \| Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Allowable-Allocation Range, Minimum	0.02
Horizon Defined Benefit Plan \| Minimum \| Alternative investments
Defined Benefit Plan Disclosure [Line Items]
Allowable-Allocation Range, Minimum	0
Horizon Defined Benefit Plan \| Maximum \| Common stocks
Defined Benefit Plan Disclosure [Line Items]
Allowable-Allocation Range, Minimum	0.88
Horizon Defined Benefit Plan \| Maximum \| Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Allowable-Allocation Range, Minimum	.4
Horizon Defined Benefit Plan \| Maximum \| Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Allowable-Allocation Range, Minimum	0.2
Horizon Defined Benefit Plan \| Maximum \| Alternative investments
Defined Benefit Plan Disclosure [Line Items]
Allowable-Allocation Range, Minimum	0.25
Community Defined Benefit Plan
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	100.00%
Percentage of Plan Assets	100.00%	100.00%
Community Defined Benefit Plan \| Common stocks
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	40.00%
Percentage of Plan Assets	39.00%	41.00%
Community Defined Benefit Plan \| Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	60.00%
Percentage of Plan Assets	61.00%	59.00%
Community Defined Benefit Plan \| Minimum \| Common stocks
Defined Benefit Plan Disclosure [Line Items]
Allowable-Allocation Range, Minimum	0.29
Community Defined Benefit Plan \| Minimum \| Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Allowable-Allocation Range, Minimum	0.49
Community Defined Benefit Plan \| Maximum \| Common stocks
Defined Benefit Plan Disclosure [Line Items]
Allowable-Allocation Range, Minimum	0.51
Community Defined Benefit Plan \| Maximum \| Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Allowable-Allocation Range, Minimum	0.71

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.

No definition available.

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Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

+ References

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- Definition

Description of target allocation percentages, or range of percentages, considering the major categories of plan assets as of the latest statement of financial position presented (on a weighted-average basis for employers with more than one plan) that are pertinent to an understanding of the plan investment policies and strategies.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(i)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (c)(i)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e2446-114920

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- Definition

Percentage of fair value of investments (categorized by debt securities, equity securities, real estate and other plan assets) to the fair value of plan assets held.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e2446-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(1)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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