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LONG-TERM DEBT (Break-Down of Long-Term Debt) (Details) - USD ($) $ in Thousands | Sep. 30, 2018 | Dec. 31, 2017 | Oct. 11, 2017 | Dec. 21, 2016 | Oct. 14, 2016 | Jun. 04, 2015 | Apr. 21, 2015
--- | --- | --- | --- | --- | --- | --- | ---
Debt Instrument [Line Items] |  |  |  |  |  |  |
Net unamortized debt issuance costs | $ (31,824) | $ (34,781) |  |  |  |  |
Less: current maturities of long term debt | (647) | (622) |  |  |  |  |
Long-term debt, net of current maturities | 2,100,825 | 2,038,321 |  |  |  |  |
Construction loan |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Net unamortized debt issuance costs | (100) |  |  |  |  |  |
6.625% senior unsecured notes due 2023 | Senior notes |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Long-term debt | 350,000 | 350,000 |  |  |  |  |
Net unamortized debt issuance costs | $ (4,600) |  |  |  |  |  |
Stated interest rate, percent | 6.625% |  |  |  |  |  | 6.625%
6.000% senior unsecured notes due 2024 | Senior notes |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Long-term debt | $ 650,000 | 650,000 |  |  |  |  |
Net unamortized debt issuance costs | $ (9,000) |  |  |  |  |  |
Stated interest rate, percent | 6.00% |  |  |  | 6.00% |  |
6.375% senior unsecured notes due 2025 | Senior notes |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Long-term debt | $ 600,000 | 600,000 |  |  |  |  |
Net unamortized debt issuance costs | $ (12,900) |  |  |  |  |  |
Stated interest rate, percent | 6.375% |  |  | 6.375% |  |  |
6.375% senior unsecured notes due 2026 | Senior notes |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Long-term debt | $ 450,000 | 450,000 |  |  |  |  |
Net unamortized debt issuance costs | $ (5,200) |  |  |  |  |  |
Stated interest rate, percent | 6.375% |  | 6.375% |  |  |  |
Nova Scotia, Amegy, KeyBank | Revolving credit agreement | Revolving credit agreement |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Long-term debt | $ 60,000 | 0 |  |  |  |  |
InterBank | Revolving credit agreement | Construction loan |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Stated interest rate, percent |  |  |  |  |  | 4.50% |
InterBank | Letter of credit | Construction loan |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Long-term debt | $ 23,296 | $ 23,724 |  |  |  |  |

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