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Supplemental Oil and Gas Disclosures - Capitalized Costs Related to Oil and Natural Gas Producing Activities (Detail) (USD $) In Thousands, unless otherwise specified | Dec. 31, 2014 | Dec. 31, 2013
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Oil and Gas Exploration and Production Industries Disclosures [Abstract] |  |
Proved oil and gas property | $ 5,156,875 us-gaap_CapitalizedCostsProvedProperties | $ 3,713,525 us-gaap_CapitalizedCostsProvedProperties
Less: Accumulated depreciation, depletion, amortization and impairment | (1,043,121)us-gaap_CapitalizedCostsAccumulatedDepreciationDepletionAmortizationAndValuationAllowanceForRelatingToOilAndGasProducingActivities | (612,380)us-gaap_CapitalizedCostsAccumulatedDepreciationDepletionAmortizationAndValuationAllowanceForRelatingToOilAndGasProducingActivities
Proved oil and gas properties, net | 4,113,754 oas_ProvedOilAndGasPropertiesNet | 3,101,145 oas_ProvedOilAndGasPropertiesNet
Unproved oil and gas properties | 809,265 us-gaap_CapitalizedCostsUnprovedProperties | 815,433 us-gaap_CapitalizedCostsUnprovedProperties
Total oil and gas properties, net | $ 4,923,019 us-gaap_CapitalizedCostsOilAndGasProducingActivitiesNet | $ 3,916,578 us-gaap_CapitalizedCostsOilAndGasProducingActivitiesNet

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- Definition Oil and Gas properties with proved reserves under the successful effort method, net of accumulated depreciation, depletion, amortization and impairment. + References No definition available. + Details
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- Definition Amount of accumulated depreciation, depletion, amortization and valuation allowance relating to oil and gas producing activities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e61901-109447 + Details
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- Definition Net amount of capitalized costs relating to oil and gas producing activities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e61901-109447 + Details
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- Definition Capitalized costs of proved properties incurred for any combination mineral interests acquisitions; wells and related equipment; support equipment and facilities; and uncompleted wells and equipment and other costs not previously disclosed within this table. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e61901-109447 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 360 -Glossary Proved Properties -URI http://asc.fasb.org/extlink&oid=6522428 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Properties -URI http://asc.fasb.org/extlink&oid=21914647 + Details
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- Definition Capitalized costs of unproved properties incurred for any combination mineral interests acquisitions and other costs not previously disclosed within this table. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e61901-109447 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Properties -URI http://asc.fasb.org/extlink&oid=21914647 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -Glossary Unproved Properties -URI http://asc.fasb.org/extlink&oid=6527831 + Details
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