Annual report pursuant to Section 13 and 15(d)

Note 5 - Acquisitions and Divestitures (Details Textual)

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Note 5 - Acquisitions and Divestitures (Details Textual) - USD ($)
$ in Thousands
 1 Months Ended 12 Months Ended
Sep. 28, 2018
Apr. 05, 2018
Dec. 31, 2019
Aug. 31, 2019
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Payments to Acquire Oil and Gas Property and Equipment, Total         $ 188,019 $ 16,782
Permian Basin [Member]              
Proceeds from Sale of Productive Assets, Total $ 56,600            
Mobile Bay Properties [Member]              
Payments to Acquire Businesses, Net of Cash Acquired, Total       $ 169,800      
Payments to Acquire Oil and Gas Property and Equipment, Cash from Long-term Lines of Credit       $ 150,000      
Magnolia Field Acquisition [Member]              
Payments to Acquire Businesses, Net of Cash Acquired, Total     $ 15,900        
Heidelberg Field [Member]              
Payments to Acquire Businesses, Net of Cash Acquired, Total   $ 16,800          
Payments to Acquire Oil and Gas Property and Equipment, Cash from Long-term Lines of Credit   $ 9,400          
Percentage of Non-operated Working Interest Acquired   9.375%          
Oil and Gas, Asset Acquisition, Amounts Included in Asset Retirement Obligations, Noncurrent, Total   $ 3,600          
Payments to Acquire Oil and Gas Property and Equipment, Total   $ 19,600