FAIR VALUE MEASUREMENTS (Measured on Recurring Basis) (Details) (Fair Value, Measurements, Recurring [Member], USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-qualified pension plan assets	$ 4,955	$ 4,905
Derivative assets, Effect of Counter-party Netting	(26,124)
Assets, Total Gross Fair Value	238,193
Assets, Net Carrying Value on Balance Sheet	212,069
Derivative, Collateral, Right to Reclaim Cash	(26,124)
Liabilities, Total Gross Fair Value	81,214
Liabilities, Net Carrying Value on Balance Sheet	55,090
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-qualified pension plan assets	4,955	4,905
Assets, Total Gross Fair Value	194,252
Liabilities, Total Gross Fair Value	0
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-qualified pension plan assets	0	0
Assets, Total Gross Fair Value	43,141
Liabilities, Total Gross Fair Value	76,663
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-qualified pension plan assets	0	0
Assets, Total Gross Fair Value	800
Liabilities, Total Gross Fair Value	4,551
Catalyst lease obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Catalyst lease obligations	55,090	53,089
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
Catalyst lease obligations [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Catalyst lease obligations	55,090	53,089
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
Commodity contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	26,124
Derivative, Collateral, Right to Reclaim Cash	(26,124)
Derivative Liability	0	30,354
Commodity contract [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	0
Derivative Liability		0
Commodity contract [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	21,573
Derivative Liability		6,989
Commodity contract [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	4,551
Derivative Liability		23,365
Derivatives included with inventory supply arrangement obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	2,473
Derivative assets, Effect of Counter-party Netting	0
Derivative assets, Net Carrying Value on Balance Sheet	2,473
Derivative Liability		177
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 Asset, Fair Value, Amount Not Offset Against Collateral	0
Derivative Liability		0
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 Asset, Fair Value, Amount Not Offset Against Collateral	2,473
Derivative Liability		177
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 Asset, Fair Value, Amount Not Offset Against Collateral	0
Derivative Liability		0
Money market funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	155,861	5,857
Money market funds [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	155,861	5,857
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
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
Commodity contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	54,075
Derivative assets, Effect of Counter-party Netting	(26,124)
Derivative assets, Net Carrying Value on Balance Sheet	27,951	10,933
Commodity contract [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	33,436
Derivative assets, Net Carrying Value on Balance Sheet		4,252
Commodity contract [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	19,839
Derivative assets, Net Carrying Value on Balance Sheet		6,681
Commodity contract [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	800
Derivative assets, Net Carrying Value on Balance Sheet		0
Derivatives included with intermediation agreement obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	20,829
Derivative assets, Effect of Counter-party Netting	0
Derivative assets, Net Carrying Value on Balance Sheet	20,829	6,016
Derivatives included with intermediation agreement obligations [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	0
Derivative assets, Net Carrying Value on Balance Sheet		0
Derivatives included with intermediation agreement obligations [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	20,829
Derivative assets, Net Carrying Value on Balance Sheet		6,016
Derivatives included with intermediation agreement obligations [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	0
Derivative assets, Net Carrying Value on Balance Sheet		$ 0