Fair Value Measurements (Details) (Fair value measured on a recurring basis, USD $) In Thousands, unless otherwise specified	Mar. 29, 2014	Dec. 31, 2013	Mar. 30, 2013
Estimated Fair Value
Fair value measurements
Cash and cash equivalents	$ 51,179	$ 88,283	$ 50,887
Auction rate security			8,808
Available for sale securities, excluding the auction rate security			116,771
Available for sale securities	138,225	118,647
Trading securities	63,412	63,215	54,377
Total assets measured at fair value	251,591	269,331	230,147
Estimated Fair Value | Foreign currency forward contracts
Fair value measurements
Derivative instruments, net	(1,613)	(684)	(247)
Estimated Fair Value | Commodity futures contracts
Fair value measurements
Derivative instruments, net	388	(130)	(449)
Level 1
Fair value measurements
Cash and cash equivalents	51,179	88,283	50,887
Trading securities	63,412	63,215	54,377
Total assets measured at fair value	114,979	151,368	104,815
Level 1 | Commodity futures contracts
Fair value measurements
Derivative instruments, net	388	(130)	(449)
Level 2
Fair value measurements
Available for sale securities, excluding the auction rate security			116,771
Available for sale securities	138,225	118,647
Total assets measured at fair value	136,612	117,963	116,524
Level 2 | Foreign currency forward contracts
Fair value measurements
Derivative instruments, net	(1,613)	(684)	(247)
Level 3
Fair value measurements
Auction rate security			8,808
Total assets measured at fair value			$ 8,808