Segment Information (Details 2) (USD $)	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011	Dec. 31, 2010
Operating income (loss)
Profit sharing	$ (8,072,000)	$ (15,203,000)
Operating income	119,816,000	205,326,000
Assets
Cash and equivalents	357,809,000	160,810,000	390,761,000	186,513,000
Investments in short-term commercial paper	64,982,000		84,830,000
Income taxes receivable	2,833,000		16,722,000
Deferred income taxes	26,089,000		25,341,000
Property, plant and equipment, net	2,199,509,000		2,193,745,000
Other	131,543,000		134,264,000
Total assets	6,043,627,000	5,827,605,000	5,979,226,000
Liabilities
Accounts payable	472,257,000		420,824,000
Income taxes payable	14,383,000		10,880,000
Deferred income taxes	500,642,000		489,915,000
Liabilities	3,637,142,000	3,599,911,000
Other
Operating income (loss)
Corporate SG and A	(7,600,000)	(9,300,000)
Company-wide stock option expense	(3,700,000)	(3,700,000)
Profit sharing	(6,500,000)	(13,300,000)
Other, net	900,000	2,000,000
Operating income	(16,862,000)	(24,256,000)
Assets
Cash and equivalents	278,200,000	149,900,000
Investments in short-term commercial paper	65,000,000	6,300,000
Income taxes receivable	2,800,000
Deferred income taxes	26,100,000	21,000,000
Property, plant and equipment, net	84,600,000	69,000,000
Debt issuance costs, net	24,000,000	22,900,000
Intra-company debt	149,600,000	147,400,000
Other	82,400,000	88,500,000
Total assets	712,673,000	504,989,000
Liabilities
Accounts payable	29,200,000	41,700,000
Income taxes payable	14,600,000	19,600,000
Accrued interest	54,500,000	61,800,000
Accrued profit sharing	6,600,000	13,600,000
Debt	2,333,600,000	2,341,000,000
Deferred income taxes	213,100,000	228,200,000
Other liabilities	80,800,000	66,900,000
Liabilities	$ 2,732,432,000	$ 2,772,754,000