Note 15 - Injection Wells Suspension (Details Textual) $ in Millions	3 Months Ended
Dec. 31, 2018 USD ($)	Jun. 30, 2019	Sep. 03, 2014
Number of Suspended Saltwater Injection Wells		2	2
Wells and Related Equipment and Facilities [Member]
Asset Impairment Charges, Total	$ 3.3

Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=109226348&loc=d3e2420-110228

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration