Fair Value Measurements (Details) (Fair value measured on a recurring basis, USD $) In Thousands, unless otherwise specified	Sep. 27, 2014	Dec. 31, 2013	Sep. 28, 2013
Estimated Fair Value
Fair value measurements
Cash and cash equivalents	$ 45,142	$ 88,283	$ 32,734
Auction rate security			10,162
Available for sale securities, excluding the auction rate security			123,391
Available for sale securities	126,870	118,647
Trading securities	69,367	63,215	58,968
Total assets measured at fair value	239,764	269,331	225,381
Estimated Fair Value | Foreign currency forward contracts
Fair value measurements
Derivative instruments, net	(1,238)	(684)	29
Estimated Fair Value | Commodity futures contracts
Fair value measurements
Derivative instruments, net	(377)	(130)	97
Level 1
Fair value measurements
Cash and cash equivalents	45,142	88,283	32,734
Trading securities	69,367	63,215	58,968
Total assets measured at fair value	114,132	151,368	91,799
Level 1 | Commodity futures contracts
Fair value measurements
Derivative instruments, net	(377)	(130)	97
Level 2
Fair value measurements
Available for sale securities, excluding the auction rate security			123,391
Available for sale securities	126,870	118,647
Total assets measured at fair value	125,632	117,963	123,420
Level 2 | Foreign currency forward contracts
Fair value measurements
Derivative instruments, net	(1,238)	(684)	29
Level 3
Fair value measurements
Auction rate security			10,162
Total assets measured at fair value			$ 10,162