Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 29, 2012	Oct. 01, 2011	Sep. 29, 2012	Oct. 01, 2011
Net income	$ 37,172	$ 41,132	$ 101,968	$ 139,921
Other comprehensive income (loss):
Pension adjustments, net of tax	742	431	2,226	1,293
Total other comprehensive income	825	497	2,789	1,626
Total comprehensive income	37,997	41,629	104,757	141,547
Natural Gas Swap [Member]
Other comprehensive income (loss):
Derivative adjustments, net of tax	83	(108)	404	(222)
Interest Rate Swap [Member]
Other comprehensive income (loss):
Derivative adjustments, net of tax	$ 0	$ 174	$ 159	$ 555