Other Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 29, 2013	Jun. 30, 2012	Jun. 29, 2013	Jun. 30, 2012
Before-Tax Amount:
Amortization of prior service cost	$ 15	$ 22	$ 30	$ 44
Amortization of actuarial loss	1,300	1,189	2,600	2,378
Total defined benefit pension plans	1,315	1,211	2,630	2,422
Loss activity recognized in other comprehensive loss	1,400	(200)	3,100	500
Other Comprehensive income (loss)	1,558	1,751	4,663	3,207
Tax (Expense) or Benefit:
Amortization of prior service cost	(6)	(8)	(12)	(16)
Amortization of actuarial loss	(504)	(461)	(1,008)	(922)
Total defined benefit pension plans	(510)	(469)	(1,020)	(938)
Loss activity recognized in other comprehensive loss	500	100	1,200	(200)
Other Comprehensive income (loss)	(604)	(678)	(1,807)	(1,243)
Net-of-Tax Amount:
Amortization of prior service cost	9	14	18	28
Amortization of actuarial loss	796	728	1,592	1,456
Total defined benefit pension plans	805	742	1,610	1,484
Total other comprehensive income	954	1,073	2,856	1,964
Natural Gas Swap [Member]
Before-Tax Amount:
Loss reclassified to net income	(244)	295	(187)	1,008
Loss activity recognized in other comprehensive loss	(97)	217	87	(483)
Total swap derivatives	(341)	512	(100)	525
Tax (Expense) or Benefit:
Loss reclassified to net income	94	(114)	72	(390)
Loss activity recognized in other comprehensive loss	38	(84)	(33)	186
Total swap derivatives	132	(198)	39	(204)
Net-of-Tax Amount:
Loss reclassified to net income	(150)	181	(115)	618
Loss activity recognized in other comprehensive loss	(59)	133	54	(297)
Total swap derivatives	(209)	314	(61)	321
Corn Option [Member]
Before-Tax Amount:
Loss reclassified to net income	(866)	0	(908)	0
Loss activity recognized in other comprehensive loss	1,450	0	3,041	0
Total swap derivatives	584	0	2,133	0
Tax (Expense) or Benefit:
Loss reclassified to net income	336	0	352	0
Loss activity recognized in other comprehensive loss	(562)	0	(1,178)	0
Total swap derivatives	(226)	0	(826)	0
Net-of-Tax Amount:
Loss reclassified to net income	(530)	0	(556)	0
Loss activity recognized in other comprehensive loss	888	0	1,863	0
Total swap derivatives	358	0	1,307	0
Interest Rate Swap [Member]
Before-Tax Amount:
Total swap derivatives	0	28	0	260
Tax (Expense) or Benefit:
Total swap derivatives	0	(11)	0	(101)
Net-of-Tax Amount:
Total swap derivatives	$ 0	$ 17	$ 0	$ 159