Quarterly report pursuant to Section 13 or 15(d)

FAIR VALUE - Narrative (Details)

v3.19.1
FAIR VALUE - Narrative (Details) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Dec. 31, 2018
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Long-term debt $ 839,229   $ 830,203
Asset retirement obligations 226 $ 184  
Second Lien Notes      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Long-term debt 692,200    
Senior Second Lien Notes Due 2023 | Estimated Fair Value      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Fair value of senior unsecured notes 723,900    
Term Loan Credit Agreement | Line of Credit      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Long-term debt $ 147,000