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FAIR VALUE OF FINANCIAL INSTRUMENTS - UNL's Securities Fair Value Hierarchy (Details) - USD ($)
Jun. 30, 2021
Dec. 31, 2020
United States [Member]    
FAIR VALUE OF FINANCIAL INSTRUMENTS    
Securities, fair value $ 1,738,576 $ (21,964)
Short-Term Investments [Member]    
FAIR VALUE OF FINANCIAL INSTRUMENTS    
Securities, fair value 7,000,000 1,000,000
Fair Value, Inputs, Level 1 [Member] | United States [Member]    
FAIR VALUE OF FINANCIAL INSTRUMENTS    
Securities, fair value 1,738,576 (21,964)
Fair Value, Inputs, Level 1 [Member] | Short-Term Investments [Member]    
FAIR VALUE OF FINANCIAL INSTRUMENTS    
Securities, fair value $ 7,000,000 $ 1,000,000