Segment Information (Details 2) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012	Dec. 31, 2011
Operating income (loss)
Profit sharing	$ (6,643,000)	$ (8,072,000)
Operating income	96,232,000	119,816,000
Assets
Cash and equivalents	477,861,000	357,809,000	375,917,000	390,761,000
Investments in short-term commercial paper			31,520,000
Deferred income taxes	23,564,000		23,449,000
Property, plant and equipment, net	2,232,413,000		2,231,198,000
Other	129,476,000		132,816,000
Total assets	5,956,574,000	6,043,627,000	5,815,416,000
Liabilities
Accounts payable	410,632,000		360,097,000
Income taxes payable	13,438,000		16,941,000
Deferred income taxes	546,722,000		537,304,000
Liabilities	3,450,570,000	3,637,142,000
Other
Operating income (loss)
Corporate SG & A	(8,000,000)	(7,600,000)
Company-wide equity- based compensation	(3,200,000)	(3,700,000)
Profit sharing	(5,900,000)	(6,500,000)
Other, net	700,000	900,000
Operating income	(16,439,000)	(16,862,000)
Assets
Cash and equivalents	445,800,000	278,200,000
Investments in short-term commercial paper		65,000,000
Deferred income taxes	23,500,000	26,100,000
Property, plant and equipment, net	74,800,000	84,600,000
Debt issuance costs	31,300,000	24,000,000
Intra-company debt	156,000,000	149,600,000
Other	90,700,000	85,200,000
Total assets	822,064,000	712,673,000
Liabilities
Accounts payable	38,800,000	29,200,000
Income taxes payable	13,400,000	14,600,000
Accrued interest	19,100,000	54,500,000
Debt	2,247,100,000	2,333,600,000
Deferred income taxes	213,800,000	213,100,000
Other	24,400,000	87,400,000
Liabilities	$ 2,556,590,000	$ 2,732,432,000