Derivative and Hedging Instruments (Details-2) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010
Regulatory Asset [Member]
Unrealized and realized gains (losses) on balance sheet [Line Items]
Beginning balance,	$ 19,230	$ 12,542
Change in unrealized loss	24,988	10,851
Realized loss reclassified to a deferred account	(3,190)	(2,868)
Realized loss reclassified to income statement	1,328	(1,295)
Ending balance,	42,356	19,230
Other Current Assets [Member]
Unrealized and realized gains (losses) on balance sheet [Line Items]
Beginning balance,	1,411	1,334
Change in unrealized loss	0	0
Realized loss reclassified to a deferred account	3,190	2,868
Realized loss reclassified to income statement	(2,997)	(2,791)
Ending balance,	$ 1,604	$ 1,411

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.

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration