FAIR VALUE MEASUREMENTS (Fair Value and Carrying Value of Debt) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014		Dec. 31, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Carrying value	$ 733,646		$ 735,576
Long-term debt, Fair value	737,590		765,657
Current portion of long-term debt	13,009		12,029
Long-Term Debt And Capital Lease Obligations, Current, Fair Value Disclosure	13,009		12,029
Long-term debt	720,637		723,547
Long-term debt, excluding current maturities, Fair value	724,581		753,628
Senior secured notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Carrying value	667,992	[1]	667,487	[1]
Long-term debt, Fair value	671,936	[1]	697,568	[1]
Long-term Line of Credit	0	[2]	15,000	[2]
Lines of Credit, Fair Value Disclosure	0	[2]	15,000	[2]
Rail Facility [Domain]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Line of Credit	8,225	[3]	0	[3]
Lines of Credit, Fair Value Disclosure	8,225	[3]	0	[3]
Catalyst lease [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Carrying value	57,429	[3]	53,089	[3]
Long-term debt, Fair value	$ 57,429	[3]	$ 53,089	[3]

[1] The estimated fair value, categorized as a Level 2 measurement, was calculated based on the present value of future expected payments utilizing implied current market interest rates based on quoted prices of the senior secured notes.

[2] The estimated fair value approximates carrying value, categorized as a Level 2 measurement, as these borrowings bear interest based upon short-term floating market interest rates.

[3] Catalyst leases are valued using a market approach based upon commodity prices for similar instruments quoted in active markets and are categorized as a Level 2 measurement. The Company has elected the fair value option for accounting for its catalyst lease repurchase obligations as the Company's liability is directly impacted by the change in fair value of the underlying catalyst.