Financial Instruments (Details 2) (USD $) In Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Reconciliation of changes in the fair value of derivatives classified as Level 3 in the fair value hierarchy
Assets balance, beginning of period	$ 9,988	$ 43,025	$ 14,912	$ 42,606
Total gains or losses:
Non-cash amortization of option premium	(7,357)	(8,070)	(14,627)	(16,049)
Other amounts included in earnings	(2,852)	10,067	(4,308)	16,853
Included in accumulated other comprehensive loss	9,850	19,464	2,488	20,752
Purchases		3,425	9,164	10,806
Settlements	2,698	(9,492)	4,698	(16,549)
Assets balance, end of period	12,327	58,419	12,327	58,419
Change in unrealized (income) loss included in earnings related to instruments still held as of the end of the period	(266)	(158)	(255)	125
Natural Gas [Member]
Reconciliation of changes in the fair value of derivatives classified as Level 3 in the fair value hierarchy
Assets balance, beginning of period	31	722	87	2,752
Total gains or losses:
Non-cash amortization of option premium	(1,470)	(1,472)	(2,924)	(2,929)
Included in accumulated other comprehensive loss	1,443	1,403	2,841	830
Assets balance, end of period	4	653	4	653
Natural Gas Liquids [Member]
Reconciliation of changes in the fair value of derivatives classified as Level 3 in the fair value hierarchy
Assets balance, beginning of period	5,053	25,498	8,350	15,641
Total gains or losses:
Non-cash amortization of option premium	(3,905)	(4,106)	(7,761)	(8,163)
Other amounts included in earnings	(3,155)	4,567	(5,098)	6,633
Included in accumulated other comprehensive loss	6,352	14,673	(510)	21,256
Purchases			7,364	7,381
Settlements	2,698	(4,395)	4,698	(6,511)
Assets balance, end of period	7,043	36,237	7,043	36,237
Change in unrealized (income) loss included in earnings related to instruments still held as of the end of the period	(174)	27	(314)	(29)
Crude Oil [Member]
Reconciliation of changes in the fair value of derivatives classified as Level 3 in the fair value hierarchy
Assets balance, beginning of period	4,904	16,805	6,475	24,213
Total gains or losses:
Non-cash amortization of option premium	(1,982)	(2,492)	(3,942)	(4,957)
Other amounts included in earnings	303	5,500	790	10,220
Included in accumulated other comprehensive loss	2,055	3,388	157	(1,334)
Purchases		3,425	1,800	3,425
Settlements		(5,097)		(10,038)
Assets balance, end of period	5,280	21,529	5,280	21,529
Change in unrealized (income) loss included in earnings related to instruments still held as of the end of the period	$ (92)	$ (185)	$ 59	$ 154

Fair Value Measurement with unobservable inputs reconciliation recurring basis asset Non cash amortization of option premium.

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- Definition

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Purchases.

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- Definition

Fair value measurement with unobservable inputs reconciliation recurring basis asset settlements.

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- Definition

Total gains or losses.

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This item represents the amount of the total change in unrealized (holding) gains or losses for the period which are included in the statement of income (or changes in net assets) in trading revenues. Such unrealized (holding) gains or losses relate to those assets still held at the reporting date for which fair value is measured on a recurring basis using significant unobservable inputs (Level 3).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 157
-Paragraph 32
-Subparagraph d

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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- Definition

This element represents total gains or losses for the period (realized and unrealized), arising from assets measured at fair value on a recurring basis using unobservable inputs (Level 3), which are included in earnings or resulted in a change in net asset value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 157
-Paragraph 32
-Subparagraph c(1)

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- Definition

This element represents total gains or losses for the period (realized and unrealized), arising from assets measured at fair value on a recurring basis using unobservable inputs (Level 3), which are included in other comprehensive income (a separate component of shareholders' equity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 157
-Paragraph 32
-Subparagraph c(1)

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- Definition

This element represents an asset measured at fair value using significant unobservable inputs (Level 3) which is required for reconciliation purposes of beginning and ending balances.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 157
-Paragraph 32
-Subparagraph c

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