Note 3 - Derivative Financial Instruments - Schedule of Location and Fair Value Amounts of All Derivative Instruments (Details) - Designated as Hedging Instrument [Member] - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Commodity Contract [Member] \| Derivative Asset - Current [Member]
Gross recognized assets	$ 26,773	$ 13,321
Gross amounts offset, assets	(1,676)	(4,461)
Derivative assets	25,097	8,860
Commodity Contract [Member] \| Derivative Liability - Current [Member]
Gross recognized liabilities	2,539	11,350
Gross amounts offset, liabilities	(1,676)	(4,461)
Derivative liabilites	863	6,889
Commodity Contract [Member] \| Derivative Assets - Noncurrent [Member]
Gross recognized assets	4,727	1,031
Gross amounts offset, assets	0	(261)
Derivative assets	4,727	770
Commodity Contract [Member] \| Derivative Liability - Noncurrent [Member]
Gross recognized liabilities	355	261
Gross amounts offset, liabilities	0	(261)
Derivative liabilites	355	0
Interest Rate Swap [Member] \| Derivative Liability - Current [Member]
Gross recognized liabilities	177	0
Gross amounts offset, liabilities	0	0
Derivative liabilites	177	0
Interest Rate Swap [Member] \| Derivative Liability - Noncurrent [Member]
Gross recognized liabilities	222	0
Gross amounts offset, liabilities	0	0
Derivative liabilites	$ 222	$ 0

Amount of obligation to return cash collateral under master netting arrangements offset against derivative assets.

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Amount of right to receive cash collateral under master netting arrangements offset against derivative liabilities.

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