Note 15 - Injection Wells Suspension (Details Textual) $ in Thousands	9 Months Ended
Sep. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2014
Number of Suspended Saltwater Injection Wells			2
Property, Plant and Equipment, Net, Ending Balance	$ 45,169	$ 43,215
Wells and Related Equipment and Facilities [Member]
Property, Plant and Equipment, Net, Ending Balance		$ 3,700
Wells and Related Equipment and Facilities [Member] \| Maximum [Member]
Tangible Asset Impairment Charges, Total	$ 3,300

Amount after accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(14))
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(8))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
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