Condensed Consolidated Statements of Income and Comprehensive Income (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Net sales	$ 712,468	$ 665,481	$ 1,383,825	$ 1,294,981
Cost of sales	(554,360)	(528,580)	(1,080,698)	(1,024,939)
Gross profit	158,108	136,901	303,127	270,042
Selling and administrative expenses	(52,868)	(48,192)	(104,810)	(96,144)
Corporate overhead	(17,736)	(16,352)	(34,624)	(31,905)
Alternative fuel mixture credits			95,500
Other expense, net	(3,646)	(4,498)	(6,225)	(8,231)
Income from operations	83,858	67,859	252,968	133,762
Interest expense, net	(13,256)	(6,321)	(22,939)	(13,224)
Income before taxes	70,602	61,538	230,029	120,538
Provision for income taxes	(25,448)	(22,170)	(167,031)	(43,753)
Net income	45,154	39,368	62,998	76,785
Weighted average common shares outstanding:
Basic	96,266	100,094	96,432	100,416
Diluted	97,411	101,128	97,596	101,518
Net income per common share:
Basic	$ 0.47	$ 0.39	$ 0.65	$ 0.76
Diluted	$ 0.46	$ 0.39	$ 0.65	$ 0.76
Dividends declared per common share	$ 0.25	$ 0.20	$ 0.50	$ 0.40
Other comprehensive income (loss), net of tax:
Fair value adjustments to cash flow hedges	(17,701)	39	(10,183)	5,722
Reclassification adjustment for cash flow hedges included in net income	1,859	(281)	1,582	(563)
Amortization of pension and postretirement plans actuarial loss and prior service cost	1,672	951	3,344	1,902
Other comprehensive income (loss)	(14,170)	709	(5,257)	7,061
Comprehensive income	$ 30,984	$ 40,077	$ 57,741	$ 83,846