Investments (Details) (USD $)																										3 Months Ended		9 Months Ended
	Sep. 29, 2012	Dec. 31, 2011	Sep. 29, 2012 Available-for-sale securities	Dec. 31, 2011 Available-for-sale securities	Sep. 29, 2012 Corporate bonds	Dec. 31, 2011 Corporate bonds	Sep. 29, 2012 Money market funds	Dec. 31, 2011 Money market funds	Sep. 29, 2012 Money market funds Denominated in Euros	Sep. 29, 2012 Money market funds Denominated in British pounds	Sep. 29, 2012 Money market funds Denominated in Canadian dollars	Sep. 29, 2012 Collateralized mortgage obligations	Dec. 31, 2011 Collateralized mortgage obligations	Sep. 29, 2012 Asset backed debt securities	Dec. 31, 2011 Asset backed debt securities	Sep. 29, 2012 U.S. Government agency securities	Dec. 31, 2011 U.S. Government agency securities	Sep. 29, 2012 U.S. Treasury securities	Dec. 31, 2011 U.S. Treasury securities	Sep. 29, 2012 Fixed rate municipal notes and bonds	Dec. 31, 2011 Fixed rate municipal notes and bonds	Sep. 29, 2012 Emerging markets debt mutual fund	Dec. 31, 2011 Emerging markets debt mutual fund	Sep. 29, 2012 Other	Dec. 31, 2011 Other	Sep. 29, 2012 Trading securities	Oct. 01, 2011 Trading securities	Sep. 29, 2012 Trading securities	Oct. 01, 2011 Trading securities	Sep. 29, 2012 High yield trading debt securities	Dec. 31, 2011 High yield trading debt securities	Sep. 29, 2012 Emerging markets trading debt mutual fund	Dec. 31, 2011 Emerging markets trading debt mutual fund	Sep. 29, 2012 Emerging markets trading debt securities	Dec. 31, 2011 Emerging markets trading debt securities	Sep. 29, 2012 Other trading debt securities	Dec. 31, 2011 Other trading debt securities
Investments
Unrealized (losses) gains related to trading securities																										$ 687,000	$ (1,800,000)	$ 1,309,000	$ (1,701,000)
Amortized Cost			344,550,000	297,916,000	132,854,000	88,589,000	84,178,000	139,420,000				24,617,000	14,915,000	22,071,000	3,533,000	20,881,000	9,720,000	20,981,000	4,848,000	20,595,000	17,718,000	17,693,000	17,693,000	680,000	1,480,000
Fair Value			348,245,000	297,443,000	135,567,000	89,146,000	84,178,000	139,420,000	12,677,000	4,917,000	3,483,000	24,816,000	15,011,000	22,131,000	3,533,000	21,094,000	9,757,000	21,036,000	4,905,000	20,631,000	17,788,000	18,109,000	16,399,000	683,000	1,484,000
Amortized Cost																														21,165,000	20,155,000	3,005,000	2,620,000	2,308,000	2,444,000	683,000	218,000
Fair Value																														22,620,000	20,750,000	3,087,000	2,487,000	2,483,000	2,355,000	772,000	221,000
Total short-term investments, amortized cost	371,711,000	323,353,000
Total short-term investments, fair value	377,207,000	323,256,000
Estimated fair value of fixed rate securities designated as available-for-sale, classified by the contractual maturity date of the security
Due within one year	42,673,000
Due after one year through three years	94,094,000
Due after three years	60,871,000
Total fixed rate securities	$ 197,638,000