Quarterly report pursuant to Section 13 or 15(d)

Asset Retirement Obligations (Details)

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Asset Retirement Obligations (Details) - USD ($)
3 Months Ended 6 Months Ended
Jun. 30, 2021
Jun. 30, 2020
Jun. 30, 2021
Jun. 30, 2020
Asset Retirement Obligations        
Beginning of period $ 30,088,000   $ 29,965,000  
Reclassify liabilities associated with assets held for sale (note 4)     (875,000)  
Accretion expense 123,000 $ 145,000 246,000 $ 289,000
End of period $ 29,336,000   $ 29,336,000