Derivatives And Risk Management (Narrative) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Derivative, Fair Value, Amount Offset Against Collateral, Net	$ 44,226	$ 62,408
Commodity Contracts [Member]
Derivative [Line Items]
Cash deposited as collateral	28,415	39,458
Letters of credit outstanding	28,500	23,000
Derivative, Fair Value, Amount Offset Against Collateral, Net	16,596	27,438
Liability position at aggregate fair value	1,376	1,336
Additional Collateral, Aggregate Fair Value	1,376	1,336
Interest Rate Swap [Member]
Derivative [Line Items]
Cash deposited as collateral	27,630	34,970
Letters of credit outstanding	3,000	5,000
Derivative, Fair Value, Amount Offset Against Collateral, Net	27,630	34,970
Liability position at aggregate fair value	55,731	73,514
Additional Collateral, Aggregate Fair Value	$ 8,600	$ 18,770

The aggregate fair value of additional assets that would be required to be posted as collateral for derivative instruments with credit-risk-related contingent features if the credit-risk-related contingent features were triggered at the end of the reporting period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4H
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624258-113959

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- Definition

The aggregate fair value of assets that are already posted, at the end of the reporting period, as collateral for derivative instruments with credit-risk-related contingent features.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4H
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624258-113959

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- Definition

The net amount as of the balance sheet date of the fair value of derivative assets and derivative liabilities that in accordance with the entity's accounting policy were offset against collateral under a master netting arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=d3e41678-113959

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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.

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- Definition

The aggregate fair value amounts of derivative instruments that contain credit-risk-related contingent features that are in a net liability position at the end of the reporting period. For nonderivative instruments that are designated and qualify as hedging instruments, the fair value amounts are the carrying value of the nonderivative hedging instrument, including the adjustment for the foreign currency transaction gain (loss) on that instrument.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4H
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624258-113959

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Balance Type:	credit
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- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

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