Description of the Business and Summary of Significant Accounting Policies (Details 4) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Rollforward of amounts included in accumulated other comprehensive loss related to fair value of financial derivative instruments that qualify for hedge accounting, net of taxes
Beginning Balance	$ (8,005)	$ (16,481)
Changes in fair value, net of deferred taxes	(632)	(4,649)
Reclassification to earnings	8,637	13,125
Ending Balance	0	(8,005)
Interest Rate Swaps [Member]
Rollforward of amounts included in accumulated other comprehensive loss related to fair value of financial derivative instruments that qualify for hedge accounting, net of taxes
Beginning Balance	(7,860)	(16,481)
Changes in fair value, net of deferred taxes	(288)	(4,312)
Reclassification to earnings	8,148	12,933
Ending Balance	0	(7,860)
Natural Gas Swaps [Member]
Rollforward of amounts included in accumulated other comprehensive loss related to fair value of financial derivative instruments that qualify for hedge accounting, net of taxes
Beginning Balance	(145)
Changes in fair value, net of deferred taxes	(344)	(337)
Reclassification to earnings	489	192
Ending Balance	$ 0	$ (145)