Fair Value Measurements (Details) (Fair value measured on a recurring basis, USD $) In Thousands, unless otherwise specified	Sep. 28, 2013	Dec. 31, 2012	Sep. 29, 2012
Estimated Fair Value
Fair value measurements
Cash and cash equivalents	$ 32,734	$ 63,862	$ 37,124
Auction rate security	10,162	9,485	8,130
Available-for-sale securities excluding the auction rate security	123,391	84,568	84,437
Trading securities	58,968	49,378	48,382
Total assets measured at fair value	225,381	207,181	178,221
Estimated Fair Value | Foreign currency forward contracts
Fair value measurements
Derivative instruments, net	29
Estimated Fair Value | Commodity futures contracts, net
Fair value measurements
Derivative instruments, net	97	(112)	48
Estimated Fair Value | Commodity option contracts
Fair value measurements
Derivative instruments, net			100
Level 1
Fair value measurements
Cash and cash equivalents	32,734	63,862	37,124
Trading securities	58,968	49,378	48,382
Total assets measured at fair value	91,799	113,128	85,654
Level 1 | Commodity futures contracts, net
Fair value measurements
Derivative instruments, net	97	(112)	48
Level 1 | Commodity option contracts
Fair value measurements
Derivative instruments, net			100
Level 2
Fair value measurements
Available-for-sale securities excluding the auction rate security	123,391	84,568	84,437
Total assets measured at fair value	123,420	84,568	84,437
Level 2 | Foreign currency forward contracts
Fair value measurements
Derivative instruments, net	29
Level 3
Fair value measurements
Auction rate security	10,162	9,485	8,130
Total assets measured at fair value	$ 10,162	$ 9,485	$ 8,130