Oil and Gas Producing Activities (Unaudited) - Assumed market prices of oil and natural gas reserves and future net revenues (Details)	12 Months Ended
Dec. 31, 2017 $ / MMcf $ / bbl	Dec. 31, 2016 $ / bbl $ / MMcf
Crude Oil
Market price:
Average sales price \| $ / bbl	0	38.34
Natural gas
Market price:
Average sales price \| $ / MMcf	0	2.56

The revenues derived from sales of oil or gas in each geographic area during the reporting period divided by the number of barrels of oil produced or thousands of cubic feet of gas produced.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher SEC
-Name Regulation S-K (SK)
-Number 229
-Section 1204
-Paragraph (b)
-Subparagraph (1)

Name:	us-gaap_AverageSalesPrices
Namespace Prefix:	us-gaap_
Data Type:	us-types:perUnitItemType
Balance Type:	na
Period Type:	duration