CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Net income (loss)	$ 118,352	$ (26,644)	$ 10,177
Other comprehensive income (loss), before tax:
Unrealized gains (losses) arising during the period	23,172	14,451	(26,938)
Amount reclassified from accumulated OCI into income	204	3,601	1,841
Total Minimum pension liability	23,376	18,052	(25,097)
Other comprehensive income (loss), before tax	23,376	18,052	(12,644)
Income tax (expense) benefit related to items of comprehensive income (loss)	(7,892)	(6,624)	4,702
Net other comprehensive income (loss)	15,484	11,428	(7,942)
Comprehensive income (loss)	133,836	(15,216)	2,235
Natural Gas Swaps [Member]
Other comprehensive income (loss), before tax:
Unrealized losses arising during the period			(533)
Amount reclassified from accumulated OCI into income			759
Unrealized gain (loss) on derivatives before tax			226
Income tax (expense) benefit related to items of comprehensive income (loss)			(80)
Net other comprehensive income (loss)			146
Interest Rate Swap [Member]
Other comprehensive income (loss), before tax:
Unrealized losses arising during the period			(447)
Amount reclassified from accumulated OCI into income			12,674
Unrealized gain (loss) on derivatives before tax			12,227
Income tax (expense) benefit related to items of comprehensive income (loss)			(4,366)
Net other comprehensive income (loss)			$ 7,861