Segment Information (Details 2) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011
Operating income (loss)
Profit sharing	$ (4,779,000)	$ (8,211,000)	$ (11,422,000)	$ (16,283,000)
Operating income	69,198,000	103,699,000	165,430,000	223,515,000
Assets
Cash and equivalents	243,753,000	420,938,000	243,753,000	420,938,000	477,861,000	375,917,000	357,809,000	390,761,000
Investments in short-term commercial paper						31,520,000
Deferred income taxes	23,682,000		23,682,000			23,449,000
Property, plant and equipment, net	2,232,852,000		2,232,852,000			2,231,198,000
Other	124,584,000		124,584,000			132,816,000
Total assets	5,735,910,000	5,971,380,000	5,735,910,000	5,971,380,000		5,815,416,000
Liabilities
Accounts payable	364,330,000		364,330,000			360,097,000
Income taxes payable	2,862,000		2,862,000			16,941,000
Accrued interest	32,509,000		32,509,000			35,306,000
Deferred income taxes	556,023,000		556,023,000			537,304,000
Liabilities	3,220,439,000	3,539,820,000	3,220,439,000	3,539,820,000
Other
Operating income (loss)
Corporate SG & A	(9,100,000)	(7,200,000)	(17,100,000)	(14,800,000)
Company-wide equity- based compensation	(2,000,000)	(2,000,000)	(5,200,000)	(5,700,000)
Profit sharing	(3,200,000)	(5,900,000)	(9,100,000)	(12,400,000)
Other, net	(100,000)	400,000	500,000	1,400,000
Operating income	(14,434,000)	(14,673,000)	(30,873,000)	(31,535,000)
Assets
Cash and equivalents	218,200,000	309,200,000	218,200,000	309,200,000
Investments in short-term commercial paper		10,000,000		10,000,000
Income taxes receivable		17,100,000		17,100,000
Deferred income taxes	23,600,000	26,900,000	23,600,000	26,900,000
Property, plant and equipment, net	73,700,000	83,900,000	73,700,000	83,900,000
Debt issuance costs	29,300,000	22,300,000	29,300,000	22,300,000
Intra-company debt	154,200,000	170,600,000	154,200,000	170,600,000
Other	105,200,000	85,700,000	105,200,000	85,700,000
Total assets	604,195,000	725,717,000	604,195,000	725,717,000
Liabilities
Accounts payable	43,500,000	28,700,000	43,500,000	28,700,000
Income taxes payable	2,900,000	2,900,000	2,900,000	2,900,000
Accrued interest	32,300,000	31,000,000	32,300,000	31,000,000
Accrued profit sharing		12,600,000		12,600,000
Debt	2,045,300,000	2,330,000,000	2,045,300,000	2,330,000,000
Deferred income taxes	205,100,000	213,000,000	205,100,000	213,000,000
Other	33,600,000	81,500,000	33,600,000	81,500,000
Liabilities	$ 2,362,721,000	$ 2,699,661,000	$ 2,362,721,000	$ 2,699,661,000