Annual report pursuant to Section 13 and 15(d)

SUPPLEMENTAL OIL AND GAS INFORMATION (UNAUDITED) - Additional Information (Details)

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SUPPLEMENTAL OIL AND GAS INFORMATION (UNAUDITED) - Additional Information (Details) - Oil
Boe in Thousands
 12 Months Ended
Dec. 31, 2020
Boe
MMBoe
Dec. 31, 2020
Boe
MMBoe
Dec. 31, 2019
Boe
MMBoe
Dec. 31, 2019
MMBoe
Boe
Dec. 31, 2018
MMBoe
Boe
Dec. 31, 2018
MMBoe
Boe
Dec. 31, 2017
Boe
Reserve Quantities [Line Items]              
Extension and discoveries attributable to successful drilling (in MMBOE) | Boe 8,306   23,662   33,241    
Proved Developed Reserves | Boe 84,145 84,145 96,634 96,634 76,216 76,216 46,346
Proved Undeveloped Reserves | Boe 38,487 38,487 66,673 66,673 59,268 59,268 29,487
Purchase of mineral in place (in MMBOE)     34,606 34.6 32,198 32.2  
Increase (decrease) to proved reserves (36,874) (36.9) (16,355) (16.4) 3,541 3.5  
Upward (downward) adjustment attributable to lower crude oil and natural gas prices (in MMBOE)   (33.8)   (9.8)   1.4  
Downward adjustment due to well performance (in MMBOE)   (0.7)   (2.0)   3.9  
Downward adjustment attributable to removal of undeveloped drilling locations (in MMBOE)   (2.3)   (4.6)   (2.8)  
Williston Basin              
Reserve Quantities [Line Items]              
Extension and discoveries attributable to successful drilling (in MMBOE)   8.3   23.7   33.2  
Proved Developed Reserves 3.1 3.1 11.3 11.3 27.6 27.6  
Additional Locations              
Reserve Quantities [Line Items]              
Proved Developed Reserves 5.2 5.2 12.3 12.3      
Proved Undeveloped Reserves         5.6 5.6