Note 8 - Commodity Derivative Activities - Summary of Gains and Losses on Derivatives (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Loss on commodity derivatives not designated as hedges	$ (1,008)	$ (981)
Commodity Contract [Member]
Loss on commodity derivatives not designated as hedges, settled	(1,760)	(384)
Gain (loss) on commodity derivatives not designated as hedges, not settled	752	(597)
Loss on commodity derivatives not designated as hedges	$ (1,008)	$ (981)

Amount of realized and unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4CC
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL109998890-113959

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624171-113959

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