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Derivative and Hedging Instruments (Details-3) (USD $) In Thousands, unless otherwise specified | 3 Months Ended
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Mar. 31, 2013 | Mar. 31, 2012
Regulatory Asset [Member] |  |
Unrealized and realized gains (losses) on balance sheet [Line Items] |  |
Beginning balance, | $ 72,329 | $ 42,356
Change in unrealized loss (gain) | (1,697) | 33,310
Realized loss reclassified to a deferred account | (290) | (2,658)
Realized gain (loss) reclassified to income statement | (1,145) | (1,494)
Ending balance, | 69,197 | 71,514
Other Current Assets [Member] |  |
Unrealized and realized gains (losses) on balance sheet [Line Items] |  |
Beginning balance, | 574 | 1,604
Change in unrealized loss (gain) | 0 | 0
Realized loss reclassified to a deferred account | 290 | 2,658
Realized gain (loss) reclassified to income statement | (605) | (3,590)
Ending balance, | $ 259 | $ 672

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- Definition Change in realized derivative gains and losses deferred. + References No definition available. + Details
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Period Type: | duration

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- Definition Realized derivative gains and losses recognized. + References No definition available. + Details
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- Definition Unrealized and realized derivative gains and losses on balance sheet. + References No definition available. + Details
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- Details
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- Definition The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of derivative instruments, including options, swaps, futures, and forward contracts, held at each balance sheet date, that was included in earnings for the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3602-108585 + Details
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