Investments Continuous Unrealized Loss Position (Details) - USD ($) $ in Thousands	Jul. 04, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
In Loss Position for Less Than 12 months, Fair Value	$ 60,749	$ 152,784
In Loss Position for Less Than 12 Months, Gross Unrealized Losses	110	126
Total Fair Value	60,749	152,784
Total Gross Unrealized Losses	110	126
U.S. treasury bills and notes
Schedule of Available-for-sale Securities [Line Items]
In Loss Position for Less Than 12 months, Fair Value	9,974
In Loss Position for Less Than 12 Months, Gross Unrealized Losses	6
Total Fair Value	9,974
Total Gross Unrealized Losses	6
Securities and obligations of U.S. government agencies
Schedule of Available-for-sale Securities [Line Items]
In Loss Position for Less Than 12 months, Fair Value	50,775	152,784
In Loss Position for Less Than 12 Months, Gross Unrealized Losses	104	126
Total Fair Value	50,775	152,784
Total Gross Unrealized Losses	$ 104	$ 126