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Fair Value (Reconciliation For All Assets And Liabilities Measured At Fair Value On A Recurring Basis Using Significant Unobservable Inputs (Level 3)) (Details) - Fair Value, Inputs, Level 3 [Member] - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended
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Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2018 | Jun. 30, 2017
Fair Value Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |
Beginning Balance | $ (12,973) | $ (18,963) | $ (16,428) | $ (19,410)
Included in regulatory assets/liabilities | 1,829 | (644) | 169 | (3,315)
Settlements | 1,314 | 1,607 | 6,429 | 4,725
Ending Balance | (9,830) | (18,000) | (9,830) | (18,000)
Natural Gas Exchange Agreements [Member] |  |  |  |
Fair Value Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |
Beginning Balance | (2,805) | (4,278) | (3,164) | (5,885)
Included in regulatory assets/liabilities | (768) | (195) | (565) | 1,817
Settlements | 93 | 300 | 249 | (105)
Ending Balance | (3,480) | (4,173) | (3,480) | (4,173)
Power Option Agreement [Member] |  |  |  |
Fair Value Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |
Beginning Balance | (5) | (266) | (19) | (76)
Included in regulatory assets/liabilities | 0 | 223 | 14 | 33
Settlements | 0 | 0 | 0 | 0
Ending Balance | (5) | (43) | (5) | (43)
Power Exchange Agreements [Member] |  |  |  |
Fair Value Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |
Beginning Balance | (10,163) | (14,419) | (13,245) | (13,449)
Included in regulatory assets/liabilities | 2,597 | (672) | 720 | (5,165)
Settlements | 1,221 | 1,307 | 6,180 | 4,830
Ending Balance | $ (6,345) | $ (13,784) | $ (6,345) | $ (13,784)

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- Definition Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Realized And Unrealized Gains Losses Included In Regulatory Assets + References No definition available. + Details
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- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. + References No definition available. + Details
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- Definition Amount of settlements of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
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- Definition Fair value of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
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