FAIR VALUE OF FINANCIAL INSTRUMENTS (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
9.0% senior secured notes due 2017
Carrying amount and estimated fair values of fixed-rate long-term debt and natural gas forward purchase contracts
Interest rate (as a percent)	9.00%
Carrying Amount | Level 1 | 9.0% senior secured notes due 2017
Carrying amount and estimated fair values of fixed-rate long-term debt and natural gas forward purchase contracts
Long-term debt	$ 497,665	$ 497,464
Carrying Amount | Level 2
Carrying amount and estimated fair values of fixed-rate long-term debt and natural gas forward purchase contracts
Natural gas forward purchase contracts liability	39	721
Fair Value | Level 1 | 9.0% senior secured notes due 2017
Carrying amount and estimated fair values of fixed-rate long-term debt and natural gas forward purchase contracts
Long-term debt	560,315	525,315
Fair Value | Level 2
Carrying amount and estimated fair values of fixed-rate long-term debt and natural gas forward purchase contracts
Natural gas forward purchase contracts liability	$ 39	$ 721