Annual report pursuant to Section 13 and 15(d)

FAIR VALUE - Assets and Liabilities Accounted For At Fair Value On A Recurring Basis (Details)

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FAIR VALUE - Assets and Liabilities Accounted For At Fair Value On A Recurring Basis (Details) - Recurring - USD ($)
$ in Thousands
Dec. 31, 2020
Dec. 31, 2019
Quoted Prices In Active Markets for Identical Assets (Liabilities) (Level 1)    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative assets (liabilities) $ 0 $ 0
Significant Other Observable Inputs (Level 2)    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative assets (liabilities) 33,664 (5,195)
Significant Unobservable Inputs (Level 3)    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative assets (liabilities) 0 0
Commodity Derivatives | Current Assets | Quoted Prices In Active Markets for Identical Assets (Liabilities) (Level 1)    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative assets (liabilities) 0 0
Commodity Derivatives | Current Assets | Significant Other Observable Inputs (Level 2)    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative assets (liabilities) 51,290 5,628
Commodity Derivatives | Current Assets | Significant Unobservable Inputs (Level 3)    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative assets (liabilities) 0 0
Commodity Derivatives | Noncurrent Assets | Quoted Prices In Active Markets for Identical Assets (Liabilities) (Level 1)    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative assets (liabilities) 0 0
Commodity Derivatives | Noncurrent Assets | Significant Other Observable Inputs (Level 2)    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative assets (liabilities) (111) 8,554
Commodity Derivatives | Noncurrent Assets | Significant Unobservable Inputs (Level 3)    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative assets (liabilities) 0 0
Commodity Derivatives | Current Liabilities | Quoted Prices In Active Markets for Identical Assets (Liabilities) (Level 1)    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative assets (liabilities) 0 0
Commodity Derivatives | Current Liabilities | Significant Other Observable Inputs (Level 2)    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative assets (liabilities) (2,504) (11,298)
Commodity Derivatives | Current Liabilities | Significant Unobservable Inputs (Level 3)    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative assets (liabilities) 0 0
Commodity Derivatives | Noncurrent Liabilities | Quoted Prices In Active Markets for Identical Assets (Liabilities) (Level 1)    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative assets (liabilities) 0 0
Commodity Derivatives | Noncurrent Liabilities | Significant Other Observable Inputs (Level 2)    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative assets (liabilities) (14,214) (8,079)
Commodity Derivatives | Noncurrent Liabilities | Significant Unobservable Inputs (Level 3)    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative assets (liabilities) 0 $ 0
Interest Rate Derivatives | Current Liabilities | Quoted Prices In Active Markets for Identical Assets (Liabilities) (Level 1)    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative assets (liabilities) 0  
Interest Rate Derivatives | Current Liabilities | Significant Other Observable Inputs (Level 2)    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative assets (liabilities) (574)  
Interest Rate Derivatives | Current Liabilities | Significant Unobservable Inputs (Level 3)    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative assets (liabilities) 0  
Interest Rate Derivatives | Noncurrent Liabilities | Quoted Prices In Active Markets for Identical Assets (Liabilities) (Level 1)    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative assets (liabilities) 0  
Interest Rate Derivatives | Noncurrent Liabilities | Significant Other Observable Inputs (Level 2)    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative assets (liabilities) (445)  
Interest Rate Derivatives | Noncurrent Liabilities | Significant Unobservable Inputs (Level 3)    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative assets (liabilities) $ 0