Income Taxes (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Taxes
Net cash paid (received) for taxes	$ 46,900,000	$ 75,900,000	$ (66,300,000)
Income tax expense (benefit)
Current income tax expense	11,334,000	128,209,000	39,554,000
Deferred income tax expense	50,451,000	30,418,000	44,306,000
Total income tax expense	61,785,000	158,627,000	83,860,000
Effective tax rate
Statutory federal tax rate (as a percent)	35.00%	35.00%	35.00%
State income taxes, net of federal benefit (as a percent)	3.40%	3.50%	3.20%
Audit settlements (as a percent)	(9.60%)
Other permanent differences (as a percent)	1.50%	(1.10%)	1.10%
Effective tax rate (as a percent)	30.30%	37.40%	39.30%
Deferred tax assets
Accrued expenses and allowances	22,714,000	31,670,000
Inventories	9,643,000	9,287,000
Other	10,680,000	3,150,000
Total deferred tax assets	43,037,000	44,107,000
Deferred tax liabilities
Property, plant and equipment	(465,273,000)	(428,699,000)
Intangible assets	(79,998,000)	(68,500,000)
Other	(11,621,000)	(11,482,000)
Total deferred tax liabilities	(556,892,000)	(508,681,000)
Net deferred tax liability	$ (513,855,000)	$ (464,574,000)