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Oil And Natural Gas Properties And Equipment (Narrative) (Details) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2016 USD ($) item | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($) | Dec. 31, 2014 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Fair value of fields |  | $ 389,231,000 | $ 412,593,000 |
Impairment of proved properties |  | $ 88,000 | 81,322,000 | $ 98,341,000
U.S. Fields [Member] |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Fair value of fields |  |  | 1,200,000 |
Impairment Of Oil And Gas Properties |  |  | 3,200,000 |
Etame Field [Member] |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Fair value of fields |  |  | 12,700,000 |
Impairment Of Oil And Gas Properties |  |  | 78,100,000 |
Etame, Ebouri, Southeast Etame and North Tchibala [Member] |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Fair value of fields |  |  |  | 41,100,000
Impairment Of Oil And Gas Properties |  |  |  | $ 98,300,000
Roosevelt County, Montana [Member] |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Impairment of Leasehold |  |  | $ 1,200,000 |
North Texas [Member] |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Number of wells, interest for sale | item | 2 |  |  |
Proceeds received from sale of property | $ 830,000 |  |  |
Impairment of proved properties | $ 100,000 |  |  |

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- Definition The adjustment to reduce the value of existing agreements that specify the lessee's rights to use the leased property. This expense is charged when the estimates of future profits generated by the leased property are reduced. + References Reference 1: 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=56944662&loc=d3e3602-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 45 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=51824106&loc=d3e2420-110228 + Details
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- Definition The aggregate amount of write-downs for impairments recognized during the period for long lived assets held for use (including those held for disposal by means other than sale). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 958 -SubTopic 225 -Section 45 -Paragraph 11 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=51659069&loc=d3e92212-112881 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Impairment -URI http://asc.fasb.org/extlink&oid=6515133 Reference 3: 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=56944662&loc=d3e3602-108585 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=51719941&loc=d3e2921-110230 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 45 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=51824106&loc=d3e2420-110228 + Details
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- Definition The expense recorded to reduce the value of oil and gas assets consisting of proved properties and unproved properties as the estimate of future successful production from these properties is reduced. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=51719941&loc=d3e2921-110230 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 360 -Section 35 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=28370743&loc=d3e66150-109466 Reference 3: 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=56944662&loc=d3e3602-108585 + Details
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- Definition The cash inflow from the sale of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 12 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3179-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Investing Activities -URI http://asc.fasb.org/extlink&oid=6516133 + Details
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- Definition Oil and Gas properties with proved reserves under the successful effort method. + References Reference 1: 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 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 360 -Section 25 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=56951519&loc=d3e64746-109465 + Details
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