Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 29, 2012	Oct. 01, 2011	Sep. 29, 2012	Oct. 01, 2011
Before-Tax Amount:
Amortization of prior service cost	$ 23	$ 23	$ 67	$ 67
Amortization of actuarial loss	1,189	681	3,567	2,043
Total defined benefit pension plans	1,212	704	3,634	2,110
Loss activity recognized in other comprehensive loss	(100)	300	(600)	500
Other Comprehensive income (loss)	1,348	814	4,555	2,656
Tax (Expense) or Benefit:
Amortization of prior service cost	(9)	(9)	(25)	(25)
Amortization of actuarial loss	(461)	(264)	(1,383)	(792)
Total defined benefit pension plans	(470)	(273)	(1,408)	(817)
Loss activity recognized in other comprehensive loss	100	100	200	200
Other Comprehensive income (loss)	(523)	(317)	(1,766)	(1,030)
Net-of-Tax Amount:
Amortization of prior service cost	14	14	42	42
Amortization of actuarial loss	728	417	2,184	1,251
Total defined benefit pension plans	742	431	2,226	1,293
Total other comprehensive income	825	497	2,789	1,626
Natural Gas Swap [Member]
Before-Tax Amount:
Loss reclassified to net income	259	103	1,267	148
Loss activity recognized in other comprehensive loss	(123)	(278)	(606)	(509)
Total swap derivatives	136	(175)	661	(361)
Tax (Expense) or Benefit:
Loss reclassified to net income	(101)	(40)	(491)	(57)
Loss activity recognized in other comprehensive loss	48	107	234	196
Total swap derivatives	(53)	67	(257)	139
Net-of-Tax Amount:
Loss reclassified to net income	158	63	776	91
Loss activity recognized in other comprehensive loss	(75)	(171)	(372)	(313)
Total swap derivatives	83	(108)	404	(222)
Interest Rate Swap [Member]
Before-Tax Amount:
Total swap derivatives	0	285	260	907
Tax (Expense) or Benefit:
Total swap derivatives	0	(111)	(101)	(352)
Net-of-Tax Amount:
Total swap derivatives	$ 0	$ 174	$ 159	$ 555