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DERIVATIVE FINANCIAL INSTRUMENTS AND FAIR VALUE MEASUREMENTS (Details) | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2018 USD ($) MMcf | Jun. 30, 2017 USD ($) | Jun. 30, 2018 USD ($) MMcf | Jun. 30, 2017 USD ($) | Dec. 31, 2017 USD ($) MMcf
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] |  |  |  |  |
Derivative, Nonmonetary Notional Amount | MMcf | 15,100 |  | 15,100 |  | 14,100
Premiums recorded in other current assets on natural gas contracts held | $ 3,600,000 |  | $ 3,600,000 |  | $ 5,500,000
Fair Value Assets, Transfers between Levels | 0 | $ 0 | 0 | $ 0 |
Long-term Debt, including current maturities | 893,671,000 |  | 893,671,000 |  | 1,193,257,000
Long-term Debt | 1,200,000,000 |  | 1,200,000,000 |  | 1,200,000,000
Fair Value, Inputs, Level 1 [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] |  |  |  |  |
Fair value, natural gas call options | 3,800,000 |  | 3,800,000 |  | 1,100,000
Fair Value, Inputs, Level 2 [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] |  |  |  |  |
Long-term Debt, Fair Value | $ 1,200,000,000 |  | $ 1,200,000,000 |  | $ 1,300,000,000

X
- Definition Aggregate notional amount of derivative expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B + Details
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- Definition Amount of transfers of assets measured on a recurring basis between levels of the fair value hierarchy. + References No definition available. + Details
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- Definition The fair value of purchased natural gas call options held. + References No definition available. + Details
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- Definition Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(16)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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