Investments (Details) - USD ($) $ in Thousands	Jul. 04, 2015	Dec. 31, 2014
Investments
Total short term investments, amortized cost	$ 628,765	$ 497,230
Total short term investments, fair value	626,537	490,566
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	980
Due after one year through three years	9,841
Due after three years	12,542
Total fixed rate securities	23,363
Available-for-sale securities.
Investments
Amortized Cost	291,768	167,049
Fair Value	291,830	167,096
Money market funds
Investments
Amortized Cost	266,106	142,432
Fair Value	266,106	142,432
Corporate bonds
Investments
Amortized Cost	12,540	11,000
Fair Value	12,538	11,015
U.S. Government agency securities
Investments
Amortized Cost	9,437	9,684
Fair Value	9,480	9,666
Other available-for-sale investments
Investments
Amortized Cost	3,685	3,933
Fair Value	3,706	3,983
Trading securities.
Investments
Amortized Cost	336,997	330,181
Fair Value	334,707	323,470
High yield trading debt securities
Investments
Amortized Cost	162,196	187,491
Fair Value	159,798	181,483
Equity mutual fund
Investments
Amortized Cost	86,309	83,809
Fair Value	84,557	82,542
Domestic equity ETF
Investments
Amortized Cost	59,155	31,307
Fair Value	61,914	32,651
Money market funds held in trading accounts
Investments
Amortized Cost	23,618	21,401
Fair Value	23,618	21,401
Other trading investments
Investments
Amortized Cost	5,719	6,173
Fair Value	4,820	$ 5,393
Denominated in British pounds \| Money market funds
Investments
Fair Value	969
Denominated in Canadian dollars \| Money market funds
Investments
Fair Value	$ 560

Line items represent reporting concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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