Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 30, 2013	Mar. 31, 2012
Net income	$ 32,405	$ 28,571
Other comprehensive income (loss):
Pension adjustments, net of tax	805	742
Total other comprehensive income	1,902	891
Total comprehensive income	34,307	29,462
Natural Gas Swap [Member]
Other comprehensive income (loss):
Derivative adjustments, net of tax	148	7
Corn Option [Member]
Other comprehensive income (loss):
Derivative adjustments, net of tax	949	0
Interest Rate Swap [Member]
Other comprehensive income (loss):
Derivative adjustments, net of tax	$ 0	$ 142