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Pension Plans And Other Postretirement Benefit Plans (Schedule Of Allocation Of Plan Assets) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 37,953	$ 33,365	$ 30,868
Other Postretirement Benefits [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		33,359
Other Postretirement Benefits [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		6
Other Postretirement Benefits [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0
Other Postretirement Benefits [Member] | Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		6
Other Postretirement Benefits [Member] | Cash Equivalents [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0
Other Postretirement Benefits [Member] | Cash Equivalents [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		6
Other Postretirement Benefits [Member] | Cash Equivalents [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0
Other Postretirement Benefits [Member] | Mutual Funds [Member] | Balanced Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	37,953	33,359
Other Postretirement Benefits [Member] | Mutual Funds [Member] | Balanced Funds [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	37,953	33,359
Other Postretirement Benefits [Member] | Mutual Funds [Member] | Balanced Funds [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefits [Member] | Mutual Funds [Member] | Balanced Funds [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plan And SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	605,652	540,914	$ 517,234
Pension Plan And SERP [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	176,225	157,503
Pension Plan And SERP [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	278,451	287,694
Pension Plan And SERP [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plan And SERP [Member] | Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	20,619	10,179
Pension Plan And SERP [Member] | Cash Equivalents [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plan And SERP [Member] | Cash Equivalents [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	20,619	10,179
Pension Plan And SERP [Member] | Cash Equivalents [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plan And SERP [Member] | Fixed Income Securities [Member] | US Government Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	20,305	30,919
Pension Plan And SERP [Member] | Fixed Income Securities [Member] | US Government Debt Securities [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plan And SERP [Member] | Fixed Income Securities [Member] | US Government Debt Securities [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	20,305	30,919
Pension Plan And SERP [Member] | Fixed Income Securities [Member] | Domestic Corporate Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	185,272	193,563
Pension Plan And SERP [Member] | Fixed Income Securities [Member] | Domestic Corporate Debt Securities [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plan And SERP [Member] | Fixed Income Securities [Member] | Domestic Corporate Debt Securities [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	185,272	193,563
Pension Plan And SERP [Member] | Fixed Income Securities [Member] | Foreign Government Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	32,054	34,145
Pension Plan And SERP [Member] | Fixed Income Securities [Member] | Foreign Government Debt Securities [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plan And SERP [Member] | Fixed Income Securities [Member] | Foreign Government Debt Securities [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	32,054	34,145
Pension Plan And SERP [Member] | Fixed Income Securities [Member] | Municipal Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	20,201	18,888
Pension Plan And SERP [Member] | Fixed Income Securities [Member] | Municipal Bonds [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plan And SERP [Member] | Fixed Income Securities [Member] | Municipal Bonds [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	20,201	18,888
Pension Plan And SERP [Member] | Mutual Funds [Member] | U.S Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	127,742	120,856
Pension Plan And SERP [Member] | Mutual Funds [Member] | U.S Equity Securities [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	127,742	120,856
Pension Plan And SERP [Member] | Mutual Funds [Member] | International Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	40,755	30,025
Pension Plan And SERP [Member] | Mutual Funds [Member] | International Equity Securities [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	40,755	30,025
Pension Plan And SERP [Member] | Mutual Funds [Member] | Absolute Return [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	7,728	6,622
Pension Plan And SERP [Member] | Mutual Funds [Member] | Absolute Return [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	7,728	6,622
Pension Plan And SERP [Member] | Common/Collective Trusts [Member] | International Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	43,462	29,140
Pension Plan And SERP [Member] | Common/Collective Trusts [Member] | Real Estate [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	34,470	19,779
Pension Plan And SERP [Member] | Partnership And Closely Held Investments [Member] | Absolute Return [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	67,167	39,077
Pension Plan And SERP [Member] | Partnership And Closely Held Investments [Member] | Private Equity Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	72	72
Pension Plan And SERP [Member] | Partnership And Closely Held Investments [Member] | Real Estate [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 5,805	$ 7,649
Minimum [Member] | Pension Plan And SERP [Member] | Common/Collective Trusts [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period	45 days
Minimum [Member] | Pension Plan And SERP [Member] | Partnership And Closely Held Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period	60 days
Maximum [Member] | Pension Plan And SERP [Member] | Common/Collective Trusts [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period	60 days
Maximum [Member] | Pension Plan And SERP [Member] | Partnership And Closely Held Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period	90 days
Investment One Partnership with NAV [Member] | Maximum [Member] | Pension Plan And SERP [Member] | Partnership And Closely Held Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period	6 years

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Fair value of assets that have been segregated and restricted to provide pension or postretirement benefits. Assets include, but are not limited to, stocks, bonds, other investments, earnings from investments, and contributions by the employer and employees.

+ 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 (b)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 6A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=SL6742756-110258

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