Investments Continuous Unrealized Loss Position (Details) (USD $) In Thousands, unless otherwise specified	Jun. 29, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
In Loss Position for Less Than 12 months, Fair Value	$ 80,499	$ 15,896
In Loss Position for Less Than 12 Months, Gross Unrealized Losses	95	57
Total Fair Value	80,499	15,896
Total Gross Unrealized Losses	95	57
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	80,499	15,896
In Loss Position for Less Than 12 Months, Gross Unrealized Losses	95	57
Total Fair Value	80,499	15,896
Total Gross Unrealized Losses	$ 95	$ 57