Note 6 - Asset Retirement Obligations (ARO) (Details Textual)	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Discounted Cash Flows Valuation Technique [Member]
Fair Value Inputs, Discount Rate	4.00%	4.00%

Interest rate used to find the present value of an amount to be paid or received in the future as an input to measure fair value. For example, but not limited to, weighted average cost of capital (WACC), cost of capital, cost of equity and cost of debt.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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