FAIR VALUE MEASUREMENTS (Measured on Recurring Basis) (Details) - USD ($) $ in Thousands | Mar. 31, 2016 | Dec. 31, 2015 |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Marketable securities | $ 234,408 | |
Fair Value, Measurements, Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Marketable securities | 234,408 | $ 234,258 |
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Marketable securities | 234,408 | 234,258 |
Non-qualified pension plan assets | 9,645 | 9,325 |
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Marketable securities | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Marketable securities | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Inventory Intermediation Agreement Obligation [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Derivative assets, gross carrying value | 365 | |
Derivative assets, effect of counter-party netting | 0 | |
Derivative assets, net carrying value | 365 | |
Fair Value, Measurements, Recurring [Member] | Inventory Intermediation Agreement Obligation [Member] | Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Derivative assets, gross carrying value | 0 | |
Fair Value, Measurements, Recurring [Member] | Inventory Intermediation Agreement Obligation [Member] | Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Derivative assets, gross carrying value | 365 | |
Fair Value, Measurements, Recurring [Member] | Inventory Intermediation Agreement Obligation [Member] | Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Derivative assets, gross carrying value | 0 | |
Fair Value, Measurements, Recurring [Member] | Catalyst lease obligations [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Derivative liability, effect of counter-party netting | 0 | 0 |
Catalyst lease obligations | 34,688 | 31,802 |
Fair Value, Measurements, Recurring [Member] | Catalyst lease obligations [Member] | Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Catalyst lease obligations | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Catalyst lease obligations [Member] | Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Catalyst lease obligations | 34,688 | 31,802 |
Fair Value, Measurements, Recurring [Member] | Catalyst lease obligations [Member] | Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Catalyst lease obligations | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Commodity contract [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Derivative liability, gross carrying value | 38,338 | 52,482 |
Derivative liability, effect of counter-party netting | (38,338) | (52,482) |
Derivative Liability | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Commodity contract [Member] | Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Derivative liability, gross carrying value | 34,368 | |
Derivative Liability | | 49,960 |
Fair Value, Measurements, Recurring [Member] | Commodity contract [Member] | Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Derivative liability, gross carrying value | 3,970 | |
Derivative Liability | | 2,522 |
Fair Value, Measurements, Recurring [Member] | Commodity contract [Member] | Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Derivative Liability | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Derivatives included with inventory supply arrangement obligations [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Derivative assets, gross carrying value | | 0 |
Derivative assets, effect of counter-party netting | | 0 |
Derivative assets, net carrying value | | 0 |
Fair Value, Measurements, Recurring [Member] | Derivatives included with inventory supply arrangement obligations [Member] | Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Derivative assets, gross carrying value | | 0 |
Fair Value, Measurements, Recurring [Member] | Derivatives included with inventory supply arrangement obligations [Member] | Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Derivative assets, gross carrying value | | 0 |
Fair Value, Measurements, Recurring [Member] | Derivatives included with inventory supply arrangement obligations [Member] | Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Derivative assets, gross carrying value | | 0 |
Fair Value, Measurements, Recurring [Member] | Money market funds [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash and cash equivalents | 507,498 | 631,280 |
Fair Value, Measurements, Recurring [Member] | Money market funds [Member] | Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash and cash equivalents | 507,498 | 631,280 |
Fair Value, Measurements, Recurring [Member] | Money market funds [Member] | Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash and cash equivalents | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Money market funds [Member] | Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash and cash equivalents | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Commodity contract [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Derivative assets, gross carrying value | 53,022 | 98,609 |
Derivative assets, effect of counter-party netting | (38,338) | (52,482) |
Derivative assets, net carrying value | 14,684 | 46,127 |
Fair Value, Measurements, Recurring [Member] | Commodity contract [Member] | Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Derivative assets, gross carrying value | 29,761 | 63,810 |
Fair Value, Measurements, Recurring [Member] | Commodity contract [Member] | Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Derivative assets, gross carrying value | 21,346 | 31,256 |
Fair Value, Measurements, Recurring [Member] | Commodity contract [Member] | Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Derivative assets, net carrying value | $ 1,915 | 3,543 |
Fair Value, Measurements, Recurring [Member] | Inventory Intermediation Agreement Obligation [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Derivative assets, gross carrying value | | 35,511 |
Derivative assets, effect of counter-party netting | | 0 |
Derivative assets, net carrying value | | 35,511 |
Fair Value, Measurements, Recurring [Member] | Inventory Intermediation Agreement Obligation [Member] | Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Derivative assets, gross carrying value | | 0 |
Fair Value, Measurements, Recurring [Member] | Inventory Intermediation Agreement Obligation [Member] | Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Derivative assets, gross carrying value | | 35,511 |
Fair Value, Measurements, Recurring [Member] | Inventory Intermediation Agreement Obligation [Member] | Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Derivative assets, gross carrying value | | $ 0 |