Oil and Gas Producing Activities (Unaudited) - Components of proved oil and gas reserves (Details) bbl in Thousands, MMcf in Thousands	Dec. 31, 2017 MMcf bbl	Dec. 31, 2016 bbl MMcf	Dec. 31, 2015 MMcf bbl
Natural Gas
Reserve Quantities [Line Items]
Proved developed reserves \| MMcf	0	4,214
Proved undeveloped reserves \| MMcf	0	0
Total proved reserves \| MMcf	0	4,214	4,835
Crude Oil
Reserve Quantities [Line Items]
Proved developed reserves \| bbl	0	187
Proved undeveloped reserves \| bbl	0	0
Total proved reserves \| bbl	0	187	226

The net quantity of proved reserves as of the balance sheet date. Proved oil reserves are the estimated quantities of crude oil and natural gas liquids which geological and engineering data demonstrate with reasonable certainty to be recoverable.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher SEC
-Name Form 20-F
-Section Item 18
-Subsection Instruction 2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 932
-SubTopic 235
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e61797-109447

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- Definition

Net quantities of an enterprise's interests in proved developed reserves of either crude oil (including condensate and natural gas liquids), natural gas, synthetic oil and gas, or other nonrenewable natural resource that is intended to be upgraded into synthetic oil and gas as of the beginning and the end of the year. "Net" quantities of reserves include those relating to the enterprise's operating and nonoperating interests in properties. Quantities of reserves relating to royalty interests owned are included in "net" quantities if the necessary information is available to the enterprise. "Net" quantities does not include reserves relating to interests of others in properties owned by the enterprise. The unit of measure for reserve quantities is defined as "barrels" for oil and synthetic oil reserves or "cubic feet" or "cubic meters" for natural gas and synthetic gas reserves.

+ References

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- Definition

Net quantities of an enterprise's interests in proved undeveloped reserves of either crude oil (including condensate and natural gas liquids), natural gas, synthetic oil and gas, or other renewable natural resource that is intended to be upgraded into synthetic oil and gas as of the beginning and the end of the year. "Net" quantities of reserves include those relating to the enterprise's operating and nonoperating interests in properties. Quantities of reserves relating to royalty interests owned are included in "net" quantities if the necessary information is available to the enterprise. "Net" quantities does not include reserves relating to interests of others in properties owned by the enterprise. The unit of measure for reserve quantities is defined as "barrels" for oil and synthetic oil reserves or "cubic feet" or "cubic meters" for natural gas and synthetic gas reserves.

+ References

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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