FAIR VALUE MEASUREMENTS (Measured on Recurring Basis) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012
Commodity contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value	$ 2,689	$ (3,751)	$ (23,365)	$ 0	$ 21,358	$ 21,358
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	5,047		4,905
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	5,047		4,905
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0		0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0		0
Fair Value, Measurements, Recurring [Member] | Catalyst lease obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Catalyst lease obligations	57,429		53,089
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	57,429		53,089
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, Fair Value, Amount Not Offset Against Collateral	13,203
Derivative, Collateral, Right to Reclaim Cash	(12,628)
Derivative Liability	575		30,354
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, Fair Value, Amount Not Offset Against Collateral	220
Derivative Liability			0
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, Fair Value, Amount Not Offset Against Collateral	12,845
Derivative Liability			6,989
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, Fair Value, Amount Not Offset Against Collateral	138
Derivative Liability			23,365
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 Liability, Fair Value, Amount Not Offset Against Collateral	1,247
Derivative, Collateral, Right to Reclaim Cash	0
Derivative Liability	1,247		177
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 Liability, Fair Value, Amount Not Offset Against Collateral	0
Derivative Liability			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 Liability, Fair Value, Amount Not Offset Against Collateral	1,247
Derivative Liability			177
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 Liability, Fair Value, Amount Not Offset Against Collateral	0
Derivative Liability			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	5,546		5,857
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	5,546		5,857
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 Asset, Fair Value, Amount Not Offset Against Collateral	33,815
Derivative assets, Effect of Counter-party Netting	(12,628)
Derivative assets, Net Carrying Value on Balance Sheet	21,187		10,933
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 Asset, Fair Value, Amount Not Offset Against Collateral	15,017
Derivative assets, Net Carrying Value on Balance Sheet			4,252
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 Asset, Fair Value, Amount Not Offset Against Collateral	15,971
Derivative assets, Net Carrying Value on Balance Sheet			6,681
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 Asset, Fair Value, Amount Not Offset Against Collateral	2,827
Derivative assets, Net Carrying Value on Balance Sheet			0
Fair Value, Measurements, Recurring [Member] | 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	15,059
Derivative assets, Effect of Counter-party Netting	0
Derivative assets, Net Carrying Value on Balance Sheet	15,059		6,016
Fair Value, Measurements, Recurring [Member] | 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
Fair Value, Measurements, Recurring [Member] | 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	15,059
Derivative assets, Net Carrying Value on Balance Sheet			6,016
Fair Value, Measurements, Recurring [Member] | 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