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Fair Value (Fair Value Of Assets And Liabilities Measured On Recurring Basis) (Details) - USD ($) $ in Thousands | Mar. 31, 2018 | Dec. 31, 2017 | Mar. 31, 2017 | Dec. 31, 2016
--- | --- | --- | --- | ---
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Gross Asset | $ 74,809 | $ 51,506 |  |
Liability | 145,975 | 161,467 |  |
Cash and cash equivalents | 26,273 | 16,172 | $ 26,179 | $ 8,507
Fixed Income Securities [Member] |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Cash and cash equivalents | 200 | 200 |  |
Fair Value, Measurements, Recurring [Member] |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Counterparty and collateral netting, assets | (60,748) | (45,308) |  |
Interest rate swaps | 13,084 | 4,903 |  |
Total | 22,534 | 14,467 |  |
Counterparty and collateral netting, liabilities | (104,974) | (107,716) |  |
Interest rate swaps | 26,470 | 35,969 |  |
Total | 41,001 | 53,751 |  |
Fair Value, Measurements, Recurring [Member] | Natural Gas Exchange Agreements [Member] |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Counterparty and collateral netting, assets | (47) | (183) |  |
Derivative Asset | 0 | 0 |  |
Counterparty and collateral netting, liabilities | (47) | (183) |  |
Derivative Liability | 2,805 | 3,164 |  |
Fair Value, Measurements, Recurring [Member] | Power Exchange Agreements [Member] |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Counterparty and collateral netting, liabilities | 0 | 0 |  |
Derivative Liability | 10,163 | 13,245 |  |
Fair Value, Measurements, Recurring [Member] | Interest Rate Swap [Member] |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Counterparty and collateral netting, assets | (1,631) | (2,574) |  |
Counterparty and collateral netting, liabilities | (29,261) | (37,544) |  |
Fair Value, Measurements, Recurring [Member] | Energy commodity derivatives [Member] |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Counterparty and collateral netting, assets | (59,064) | (42,550) |  |
Derivative Asset | 961 | 1,264 |  |
Counterparty and collateral netting, liabilities | (75,660) | (69,988) |  |
Derivative Liability | 1,558 | 1,354 |  |
Fair Value, Measurements, Recurring [Member] | Power Option Agreement [Member] |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Counterparty and collateral netting, liabilities | 0 | 0 |  |
Derivative Liability | 5 | 19 |  |
Fair Value, Measurements, Recurring [Member] | Foreign Exchange Contract [Member] |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Counterparty and collateral netting, assets | (6) | (1) |  |
Derivative Asset | 16 | 31 |  |
Counterparty and collateral netting, liabilities | (6) | (1) |  |
Derivative Liability | 0 | 0 |  |
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Total | 8,473 | 8,269 |  |
Total | 0 | 0 |  |
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Interest rate swaps | 14,715 | 7,477 |  |
Total | 74,762 | 51,323 |  |
Interest rate swaps | 55,731 | 73,513 |  |
Total | 132,955 | 144,856 |  |
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Energy commodity derivatives [Member] |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Gross Asset | 60,025 | 43,814 |  |
Liability | 77,218 | 71,342 |  |
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Foreign Exchange Contract [Member] |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Gross Asset | 22 | 32 |  |
Liability | 6 | 1 |  |
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Total | 47 | 183 |  |
Total | 13,020 | 16,611 |  |
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Natural Gas Exchange Agreements [Member] |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Gross Asset | 47 | 183 |  |
Liability | 2,852 | 3,347 |  |
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Power Exchange Agreements [Member] |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Liability | 10,163 | 13,245 |  |
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Power Option Agreement [Member] |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Liability | 5 | 19 |  |
Fixed Income Funds [Member] | Fair Value, Measurements, Recurring [Member] |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Deferred compensation assets: | 1,663 | 1,638 |  |
Fixed Income Funds [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member] |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Deferred compensation assets: | 1,663 | 1,638 |  |
Equity Funds [Member] | Fair Value, Measurements, Recurring [Member] |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Deferred compensation assets: | 6,810 | 6,631 |  |
Equity Funds [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member] |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Deferred compensation assets: | $ 6,810 | $ 6,631 |  |

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- Definition Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section 45 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=82887183&loc=d3e6676-107765 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3044-108585 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.1) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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