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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, 2017 | Jun. 30, 2016 | Jun. 30, 2017 | Jun. 30, 2016
Fair Value Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |
Beginning Balance | $ (18,963) | $ (26,296) | $ (19,410) | $ (27,124)
Included in regulatory assets/liabilities | (644) | 2,841 | (3,315) | (1,309)
Settlements | 1,607 | 1,879 | 4,725 | 6,857
Ending Balance | (18,000) | (21,576) | (18,000) | (21,576)
Natural Gas Exchange Agreements [Member] |  |  |  |
Fair Value Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |
Beginning Balance | (4,278) | (6,006) | (5,885) | (5,039)
Included in regulatory assets/liabilities | (195) | (1,551) | 1,817 | (3,296)
Settlements | 300 | 700 | (105) | 1,478
Ending Balance | (4,173) | (6,857) | (4,173) | (6,857)
Power Option Agreement [Member] |  |  |  |
Fair Value Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |
Beginning Balance | (266) | (97) | (76) | (124)
Included in regulatory assets/liabilities | 223 | (8) | 33 | 19
Settlements | 0 | 0 | 0 | 0
Ending Balance | (43) | (105) | (43) | (105)
Power Exchange Agreements [Member] |  |  |  |
Fair Value Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |
Beginning Balance | (14,419) | (20,193) | (13,449) | (21,961)
Included in regulatory assets/liabilities | (672) | 4,400 | (5,165) | 1,968
Settlements | 1,307 | 1,179 | 4,830 | 5,379
Ending Balance | $ (13,784) | $ (14,614) | $ (13,784) | $ (14,614)

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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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