Quarterly report pursuant to Section 13 or 15(d)

EQUITY INVESTMENTS (Narrative) (Details)

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EQUITY INVESTMENTS (Narrative) (Details)
a in Thousands
 3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2020
USD ($)
Sep. 30, 2021
USD ($)
a
Sep. 30, 2020
USD ($)
Dec. 31, 2019
USD ($)
May 17, 2021
USD ($)
Dec. 31, 2020
USD ($)
Mar. 31, 2020
USD ($)
Schedule of Equity Method Investments [Line Items]              
Equity investments   $ 0     $ 0 $ 24,816,000  
Investment in Grizzly Oil Sands ULC              
Schedule of Equity Method Investments [Line Items]              
Equity investment, ownership interest   24.50%          
Amount of cash paid for equity investments       $ 0      
Increase (decrease) due to foreign currency translation adjustment $ 3,700,000   $ (4,100,000)        
Equity investments         $ 0 24,816,000  
Investment in Mammoth Energy              
Schedule of Equity Method Investments [Line Items]              
Equity investments           $ 0 $ 0
Athabasca, Peace River And Cold Lake Oil Sands Regions | Investment in Grizzly Oil Sands ULC              
Schedule of Equity Method Investments [Line Items]              
Gas and oil area, reserve (in acres) | a   830