Fair Value Measurements (Details) (Fair Value, Measurements, Recurring [Member], USD $) In Thousands, unless otherwise specified	Jun. 28, 2014	Dec. 31, 2013	Jun. 29, 2013
Estimate of Fair Value Measurement [Member]
Fair value measurements
Cash and cash equivalents	$ 57,091	$ 88,283	$ 31,946
Auction rate security			10,162
Available for sale securities, excluding the auction rate security			127,704
Available for sale securities	132,688	118,647
Trading securities	68,582	63,215	55,753
Total assets measured at fair value	258,592	269,331	224,583
Estimate of Fair Value Measurement [Member] | Foreign Exchange Forward [Member]
Fair value measurements
Derivative instruments, net	81	(684)	(759)
Estimate of Fair Value Measurement [Member] | Commodity Futures [Member]
Fair value measurements
Derivative instruments, net	150	(130)	(223)
Fair Value, Inputs, Level 1 [Member]
Fair value measurements
Cash and cash equivalents	57,091	88,283	31,946
Trading securities	68,582	63,215	55,753
Total assets measured at fair value	125,823	151,368	87,476
Fair Value, Inputs, Level 1 [Member] | Commodity Futures [Member]
Fair value measurements
Derivative instruments, net	150	(130)	(223)
Fair Value, Inputs, Level 2 [Member]
Fair value measurements
Available for sale securities, excluding the auction rate security			127,704
Available for sale securities	132,688	118,647
Total assets measured at fair value	132,769	117,963	126,945
Fair Value, Inputs, Level 2 [Member] | Foreign Exchange Forward [Member]
Fair value measurements
Derivative instruments, net	81	(684)	(759)
Fair Value, Inputs, Level 3 [Member]
Fair value measurements
Auction rate security			10,162
Total assets measured at fair value			$ 10,162