Other Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 30, 2013	Mar. 31, 2012
Before-Tax Amount:
Amortization of prior service cost	$ 15	$ 22
Amortization of actuarial loss	1,300	1,189
Total defined benefit pension plans	1,315	1,211
Loss activity recognized in other comprehensive loss	1,800	700
Other Comprehensive income (loss)	3,105	1,456
Tax (Expense) or Benefit:
Amortization of prior service cost	(6)	(8)
Amortization of actuarial loss	(504)	(461)
Total defined benefit pension plans	(510)	(469)
Loss activity recognized in other comprehensive loss	700	(300)
Other Comprehensive income (loss)	(1,203)	(565)
Net-of-Tax Amount:
Amortization of prior service cost	9	14
Amortization of actuarial loss	796	728
Total defined benefit pension plans	805	742
Total other comprehensive income	1,902	891
Natural Gas Swap [Member]
Before-Tax Amount:
Loss reclassified to net income	57	713
Loss activity recognized in other comprehensive loss	184	(700)
Total swap derivatives	241	13
Tax (Expense) or Benefit:
Loss reclassified to net income	(22)	(276)
Loss activity recognized in other comprehensive loss	(71)	270
Total swap derivatives	(93)	(6)
Net-of-Tax Amount:
Loss reclassified to net income	35	437
Loss activity recognized in other comprehensive loss	113	(430)
Total swap derivatives	148	7
Corn Option [Member]
Before-Tax Amount:
Loss reclassified to net income	(42)	0
Loss activity recognized in other comprehensive loss	1,591	0
Total swap derivatives	1,549	0
Tax (Expense) or Benefit:
Loss reclassified to net income	16	0
Loss activity recognized in other comprehensive loss	(616)	0
Total swap derivatives	(600)	0
Net-of-Tax Amount:
Loss reclassified to net income	(26)	0
Loss activity recognized in other comprehensive loss	975	0
Total swap derivatives	949	0
Interest Rate Swap [Member]
Before-Tax Amount:
Total swap derivatives	0	232
Tax (Expense) or Benefit:
Total swap derivatives	0	(90)
Net-of-Tax Amount:
Total swap derivatives	$ 0	$ 142