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ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Other Comprehensive Income (Loss) Before Reclassifications, Unrealized Gains (Losses) on Risk-Management Assets/Liabilities | $ (5,673) | $ (35,013) |
Other Comprehensive (Income) Loss Before Reclassification, Pension and Postretirement Benefit Plan Obligations | (8,116) | (12,337) |
Other Comprehensive Income (Loss) Before Reclassification, Unrealized Gains (Losses) on Risk-Management Assets/Liabilities of Unconsolidated Affiliates | 2,396 | (409) |
Other comprehensive income (loss) before reclassifications | (11,393) | (47,759) |
Other Comprehensive Income (Loss) Reclassification Adjustment from AOCI for Unrealized Gains (Losses) on Risk-Management Assets/Liabilities, Net of Tax | 36,870 | 63,687 | $ (6,977)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Other Comprehensive Income Attributable to Equity Method Investments, Net of Tax | (28) | (164) |
Other Comprehensive Income (Loss), Reclassification Adjustment included in Net Income, Net of Tax | 49,785 | 53,867 | 5,550
Impact of Merger Transaction On Unrealized Gains (Losses) on Risk Management Assets/Liabilities |  | (40,288) |
Impact of Merger Transaction on Pension and Postretirement Benefit Plan Obligations |  | 0 |
Impact of Merger Transaction on Unrealized Gains (Losses) on Risk Management Assets/Liabilities of Unconsolidated Affiliates |  | 0 |
Impact of Merger Transaction on AOCI, Total |  | (40,288) |
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax, Portion Attributable to Parent | 31,197 | (29,760) |
Other Comprehensive (Income) Loss, Pension and Postretirement Benefit Plans, after Reclassification Adjustment, after Tax | 4,771 | (4,175) | (16,693)
Other Comprehensive Income (Loss) on investment in unconsolidated affiliates | 2,424 | (245) |
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent | 38,392 | (34,180) |
Impact of Adoption of ASU 2018-02 on Unrealized Gains (Losses) on Risk Management Assets/Liabilities | (17,020) |  |
Impact of Adoption of ASU 2018-02 on Pension and Postretirement Benefit Plan Obligations | (20,340) |  |
Impact of Adoption of ASU 2018-02 on Unrealized Gains (Losses) on Risk Management Assets/Liabilities of Unconsolidated Affiliates | (741) |  |
Impact of Adoption of ASU 2018-02 on AOCI, Total | (38,101) |  |
Unrealized gains (losses) on risk management assets/liabilities - December 31 | (64,660) | (81,915) | (52,155)
Pension and Postretirement Benefit Plan Obligations - December 31 | (121,785) | (105,411) | (101,236)
Unrealized gains (losses) on risk-management assets/liabilities of unconsolidated affiliates - December 31 | (1,794) | (1,204) | (959)
Accumulated other comprehensive loss - December 31 | (188,239) | (188,530) | (154,350)
Beginning balance adjustments on unrealized gains (losses) on risk management assets/liabilities |  | 3,078 |
Beginning balance adjustments on pension and postretirement benefit plan obligations |  | (805) |
Beginning balance adjustments on unrealized gains (losses) on risk-management asset/liabilities of unconsolidated affiliates |  | (2,273) |
Beginning balance adjustments on accumulated other comprehensive loss |  | 0 |
Reclassification Adjustment from AOCI on Risk Management Assets/Liabilities, Income Tax | 11,013 | 26,899 | (230)
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member] |  |  |
Other Comprehensive Income (Loss) Reclassification Adjustment from AOCI for Unrealized Gains (Losses) on Risk-Management Assets/Liabilities, Net of Tax | 36,870 | 45,541 | (676)
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member] | Sales [Member] | Commodity Contract [Member] |  |  |
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income | (29,596) | (69,561) | 26,422
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member] | Interest Expense [Member] | Interest Rate Contracts |  |  |
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income | (18,287) | (21,025) | (19,215)
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member] | Total before tax [Member] |  |  |
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income | (47,883) | (90,586) | 7,207
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member] | Tax Expense [Member] |  |  |
Reclassification Adjustment from AOCI on Risk Management Assets/Liabilities, Income Tax | 11,013 | 26,899 | (230)
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member] | Net of tax [Member] |  |  |
Other Comprehensive Income (Loss) Reclassification Adjustment from AOCI for Unrealized Gains (Losses) on Risk-Management Assets/Liabilities, Net of Tax | 36,870 | 63,687 | (6,977)
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member] | Net income attributable to noncontrolling interest [Member] |  |  |
Reclassification Adjustment from AOCI on Risk Management Assets/Liabilities Net of Tax, Portion Attributable to Noncontrolling Interest | 0 | (18,146) | 6,301
Accumulated Pension and Postretirement Benefit Plans Adjustment Attributable to Parent [Member] |  |  |
Other Comprehensive (Income) Loss, Pension and Postretirement Benefit Plans, Reclassification Adjustment from AOCI, After Tax | (12,887) | (8,162) | (6,210)
Pension and Postretirement Benefit Plans, Amortization of Gain (Loss) | (18,398) | (15,265) | (12,012)
Pension and Postretirement Benefit Plans, Amortization of Prior Service Cost (Credit) | 1,662 | 1,662 | 1,662
Reclassification Adjustment from AOCI, before Tax, Pension and Postretirement Benefit Plans, Gain (Loss) | (16,736) | (13,603) | (10,350)
Reclassification Adjustment from AOCI, Tax, Pensions and Postretirement Benefit Plans, Gain (Loss) | 3,849 | 5,441 | 4,140
Accumulated Other Comprehensive Income from Investments in Unconsolidated Affiliates Attributable to Parent [Member] |  |  |
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Other Comprehensive Income Attributable to Equity Method Investments, Net of Tax | (28) | (164) | (16)
Reclassification Adjustment from AOCI, Before Tax, Portion Attributable to Unconsolidated Affiliates | (36) | (367) | (63)
Reclassification Adjustment from AOCI, Tax, Portion Attributable to Unconsolidated Affiliates | 8 | 97 | 10
Accumulated Other Comprehensive Income from Investments in Unconsolidated Affiliates Attributable to Parent [Member] | Net of tax [Member] |  |  |
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Other Comprehensive Income Attributable to Equity Method Investments, Net of Tax | (28) | (270) | (53)
Reclassification Adjustment from AOCI, Net of Tax, Portion Attributable to Unconsolidated Affiliates | 0 | $ (106) | $ (37)
Cash Flow Hedging [Member] | Commodity Contract [Member] |  |  |
Unrealized Gain Loss On Cash Flow Hedges Net Of Tax Accumulated Other Comprehensive Income Loss | 37,589 |  |
Commodity Cash Flow Hedge Unrealized Gain (Loss) to be Reclassified During Next 12 Months | 37,500 |  |
Commodity Cash Flow Hedge Gain Loss To Be Reclassified After Next 12 Months Net | 100 |  |
Cash Flow Hedging [Member] | Interest Rate Contracts |  |  |
Amount of accumulated other comprehensive income (loss) attributable primarily to settled interest-rate swaps. | (40,037) |  |
Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net | (13,500) |  |
Cash Flow Hedging [Member] | Forward Contracts [Member] |  |  |
Amount of accumulated other comprehensive income (loss) attributable primarily to forward starting interest-rate swaps. | $ (62,212) |  |

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