Derivative Instruments/Hedging (Details 3) (Derivatives not designated as hedging instruments, USD $) In Thousands, unless otherwise specified	Jun. 30, 2013
Fair values of derivatives
Estimated fair value of derivative assets	$ 10,351
Estimated fair value of derivative liabilities	59
Oil contracts \| Current assets
Fair values of derivatives
Estimated fair value of derivative assets	1,151
Oil contracts \| Current liabilities
Fair values of derivatives
Estimated fair value of derivative liabilities	59
Natural gas contracts \| Current assets
Fair values of derivatives
Estimated fair value of derivative assets	6,805
Natural gas contracts \| Noncurrent assets
Fair values of derivatives
Estimated fair value of derivative assets	$ 2,395

Fair value of the gross liabilities less the gross assets of a derivative liability or group of derivative liabilities.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 10

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13433-108611

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 45

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 15

-URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13495-108611

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 45

-Paragraph 6

-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant