Note 16 - Supplemental Oil and Gas Disclosures (Unaudited) - Cost Incurred (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Development costs	$ 131,271	$ 94,478	$ 18,262
Exploration costs		8,509	12,529
Property acquisition costs	41,465	31,409
	$ 172,736	$ 134,396	$ 30,791

Cost incurred, including capitalized costs and costs charged to expense, in acquisition of oil and gas properties.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 932
-SubTopic 235
-Section 50
-Paragraph 18
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Costs incurred, including capitalized costs and costs charged to expense, associated with the acquisition of oil and gas properties that have proved reserves.

+ References

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-Publisher FASB
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Development costs incurred, including capitalized costs and costs charged to expense, in oil and gas activities.

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Exploration costs incurred, including capitalized costs and costs charged to expense, in oil and gas activities.

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-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
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