FAIR VALUE MEASUREMENTS (Fair Value and Carrying Value of Debt) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Carrying value	$ 711,548		$ 709,980
Long-term debt, Fair value	748,748		744,405
Less: Current maturities, Carrying value	0		0
Less: Current maturities, Fair value	0		0
Long-term debt	711,548		709,980
Long-term debt, excluding current maturities, Fair value	748,748		744,405
Senior secured notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Carrying value	666,768	[1]	666,538	[1]
Long-term debt, Fair value	703,968	[1]	700,963	[1]
Catalyst lease [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Carrying value	44,780	[2]	43,442	[2]
Long-term debt, Fair value	$ 44,780	[2]	$ 43,442	[2]

[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] Catalyst leases are valued using a market approach based upon future commodity prices for similar instruments quoted in active markets and is classified as a Level 2 measurement.