FAIR VALUE OF FINANCIAL INSTRUMENTS (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Carrying amount and estimated fair values of fixed-rate long-term debt and natural gas forward purchase contracts
Long-term debt	$ 526,563	$ 497,464
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%
ABL revolver expires 2016
Carrying amount and estimated fair values of fixed-rate long-term debt and natural gas forward purchase contracts
Long-term debt	29,000
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	497,563
Long-term debt	29,000	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	2,084	721
Carrying Amount | Level 2 | ABL revolver expires 2016
Carrying amount and estimated fair values of fixed-rate long-term debt and natural gas forward purchase contracts
Long-term debt	29,000
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	556,250	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	2,084	721
Fair Value | Level 2 | ABL revolver expires 2016
Carrying amount and estimated fair values of fixed-rate long-term debt and natural gas forward purchase contracts
Long-term debt	$ 29,000