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Note 8 - Commodity Derivative Activities - Reconciliation of Gross Amounts to Amounts as Presented on Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Fair value of oil and natural gas derivatives - Current Assets	$ 1,826	$ 803
Fair value of oil and natural gas derivatives - Current Liabilities	(742)
Fair value of oil and natural gas derivatives - Non-current Liabilities	0	$ (471)
Not Designated as Hedging Instrument [Member] \| Commodity Contract [Member]
Fair value of oil and natural gas derivatives - Current Assets	1,826
Fair value of oil and natural gas derivatives - Non-current Assets
Fair value of oil and natural gas derivatives - Current Liabilities	(742)
Fair value of oil and natural gas derivatives - Non-current Liabilities
Total	1,084
Not Designated as Hedging Instrument [Member] \| Commodity Contract [Member] \| Fair Value, Inputs, Level 1 [Member]
Fair value of oil and natural gas derivatives - Current Assets
Fair value of oil and natural gas derivatives - Non-current Assets
Fair value of oil and natural gas derivatives - Current Liabilities
Fair value of oil and natural gas derivatives - Non-current Liabilities
Total
Not Designated as Hedging Instrument [Member] \| Commodity Contract [Member] \| Fair Value, Inputs, Level 2 [Member]
Fair value of oil and natural gas derivatives - Current Assets	1,826
Fair value of oil and natural gas derivatives - Non-current Assets
Fair value of oil and natural gas derivatives - Current Liabilities	(742)
Fair value of oil and natural gas derivatives - Non-current Liabilities
Total	1,084
Not Designated as Hedging Instrument [Member] \| Commodity Contract [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair value of oil and natural gas derivatives - Current Assets
Fair value of oil and natural gas derivatives - Non-current Assets
Fair value of oil and natural gas derivatives - Current Liabilities
Fair value of oil and natural gas derivatives - Non-current Liabilities
Total