Annual report pursuant to Section 13 and 15(d)

FAIR VALUE - Narrative (Details)

v3.20.4
FAIR VALUE - Narrative (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Asset retirement obligations $ 0.7  
Estimated Fair Value | Unsecured Ven Bakken Note    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair value of long-term debt 129.3 $ 130.0
Estimated Fair Value | Second Lien Notes | Quoted Prices In Active Markets for Identical Assets (Liabilities) (Level 1)    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair value of second lien notes $ 256.1 $ 434.4