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ACCOUNTS PAYABLE AND ACCRUED LIABILITIES - Additional Information (Details) - USD ($)
$ in Millions
Dec. 31, 2020
Jun. 30, 2020
Accounts Payable and Accrued Liabilities [Abstract]    
Present value of asset retirement obligation $ 17.2 $ 17.3
Undiscounted value of asset retirement obligation $ 18.1 $ 18.7