Quarterly report pursuant to Section 13 or 15(d)

FAIR VALUE - Narrative (Details)

v3.21.1
FAIR VALUE - Narrative (Details) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2021
Dec. 31, 2020
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Asset retirement obligations incurred and acquired $ 0.2  
Second Lien Notes due 2023 | Estimated Fair Value | Second Lien Notes    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fair value of long-term debt 16.0 $ 256.1
Unsecured Notes due 2028 | Estimated Fair Value | Unsecured Debt    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fair value of long-term debt $ 547.3