Quarterly report pursuant to Section 13 or 15(d)

LONG-TERM DEBT - Schedule of Debt (Details)

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LONG-TERM DEBT - Schedule of Debt (Details) - USD ($)
$ in Thousands
Mar. 31, 2021
Dec. 31, 2020
Debt Instrument [Line Items]    
Principal Balance $ 828,669 $ 949,755
Unamortized debt discounts and premiums 140 2,041
Unamortized debt issuance costs (11,748) (6,953)
Total debt 817,061 944,843
Less current portion of long-term debt 0 (65,000)
Total long-term debt 817,061 879,843
Unsecured Notes due 2028 | Unsecured Debt    
Debt Instrument [Line Items]    
Principal Balance 550,000 0
Second Lien Notes due 2023 | Second Lien Notes    
Debt Instrument [Line Items]    
Principal Balance 15,669 287,755
Unsecured VEN Bakken Note due 2022 | Unsecured Debt    
Debt Instrument [Line Items]    
Principal Balance 0 130,000
Revolving Credit Facility    
Debt Instrument [Line Items]    
Principal Balance 263,000 532,000
Revolving Credit Facility | Other Noncurrent Assets, Net    
Debt Instrument [Line Items]    
Unamortized debt issuance costs $ (6,100) $ (6,500)