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This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

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Fair values as of the balance sheet date of all assets resulting from contracts that meet the criteria of being accounted for as derivative instruments, net of the effects of master netting arrangements.

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Derivative instrument obligations meeting the definition of a liability which the Company is a party to as of the balance sheet date.

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The net amount of all regulatory assets less all regulatory liabilities as of the end of the period.

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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.

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FAIR VALUE MEASUREMENTS (Details) (USD $) In Thousands									6 Months Ended
FAIR VALUE MEASUREMENTS (Details) (USD $) In Thousands	Jun. 30, 2011	Dec. 31, 2010	Jun. 30, 2011 Fair Value, Measurements, Recurring [Member] Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]	Dec. 31, 2010 Fair Value, Measurements, Recurring [Member] Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]	Jun. 30, 2011 Fair Value, Measurements, Recurring [Member] Significant Other Observable Inputs (Level 2) [Member]	Dec. 31, 2010 Fair Value, Measurements, Recurring [Member] Significant Other Observable Inputs (Level 2) [Member]	Jun. 30, 2011 Fair Value, Measurements, Recurring [Member] Significant Unobservable Inputs (Level 3) [Member]	Dec. 31, 2010 Fair Value, Measurements, Recurring [Member] Significant Unobservable Inputs (Level 3) [Member]	Jun. 30, 2011 Net derivative assets/(liabilities) [Member]	Jun. 30, 2011 Contracts For Differences [Member]
Assets:
Derivative assets	$ 84,294	$ 34,188	$ 0	$ 0	$ 0	$ 0	$ 84,294	$ 34,188
Noncurrent investments available for sale	10,111	9,774	10,111	9,774	0	0	0	0
Deferred Compensation Plan	3,694	3,725	3,694	3,725	0	0	0	0
Supplemental retirement benefit trust life insurance policies (Note G)	5,930	5,665	5,930	5,665	0	0	0	0
Total financial assets, fair value	104,029	53,352	19,735	19,164	0	0	84,294	34,188
Liabilities:
Derivative liabilities	269,506	142,806	0	0	0	0	269,506	142,806
Net fair value assets/(liabilities)	(165,477)	(89,454)	19,735	19,164	0	0	(185,212)	(108,618)
Changes in fair value of assets and liabilities classified as level 3 [Roll Forward]
Net assets/(liabilities)	(185,212)								(108,618)
Unrealized gains and (losses), net
Included in earnings									(408)
Included in other comprehensive income									90
Included in regulatory assets/(liabilities)									(76,276)
Net assets/(liabilities)	(185,212)
Change in unrealized gains (losses), net relating to net derivative assets/(liabilities), still held as of end of period									(76,594)
Change in net regulatory asset/(liability) balance [Roll Forward]
Net regulatory assets/(liabilities)	185,252									108,976
Unrealized (gains) and losses, net										76,276
Net regulatory assets/(liabilities)	$ 185,252