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Derivative Financial Instruments - Notional Amounts and Estimated Fair Values of Outstanding Derivative Positions (Detail) (USD $) In Thousands, unless otherwise specified |  |  | 6 Months Ended |
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Jun. 30, 2014 | Jun. 30, 2013 | Jun. 30, 2014 Oil [Member] | Jun. 30, 2014 Natural Gas [Member] | Jun. 30, 2014 Other Liabilities [Member] | Jun. 30, 2014 Other Assets [Member]
Derivatives, Fair Value [Line Items] |  |  |  |  |  |
Notional Units |  |  | Barrels | MMBTUs |  |
Derivative assets, Notional Amount |  |  | $ 452 | $ 1,625 |  |
Derivative assets, Estimated Fair Value | 3,653 | 2,200 | 1,701 | 1,952 |  | 3,653
Derivative liabilities, Notional Amount |  |  | (452) | (1,625) |  |
Derivative liabilities, Estimated Fair Value | $ (2,084) | $ (991) | $ (1,207) | $ (877) | $ 2,084 |

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- Definition Fair value of financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, elected not to be offset against an obligation to return collateral under a master netting arrangement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=20225523&loc=SL20225862-175312 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 8 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=7476318&loc=d3e41678-113959 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 55 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=28370219&loc=SL20226011-175313 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 55 -Paragraph 9 -URI http://asc.fasb.org/extlink&oid=28370219&loc=SL20226006-175313 + Details
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