Fair Value Measurements (Details 4) (USD $) In Thousands, unless otherwise specified								6 Months Ended
	Jun. 29, 2013	Dec. 31, 2012	Jun. 30, 2012	Jun. 29, 2013 Cost Basis Level 2	Jun. 30, 2012 Cost Basis Level 2	Jun. 29, 2013 Estimated Fair Value Level 2	Jun. 30, 2012 Estimated Fair Value Level 2	Jun. 29, 2013 Auction rate security Level 3	Jun. 30, 2012 Auction rate security Level 3	Dec. 31, 2011 Auction rate security Level 3
Level 3 reconciliation
Balance at the beginning of the period								$ 9,485	$ 7,453	$ 7,453
Unrealized loss in other comprehensive earnings								677
Balance at the end of the period								10,162	7,453	7,453
Industrial revenue development bonds, carrying amount, approximates fair value	$ 7,500	$ 7,500	$ 7,500	$ 7,500	$ 7,500	$ 7,500	$ 7,500