Cash, Cash Equivalents and Investments (Details 2) (USD $) In Thousands, unless otherwise specified	Sep. 27, 2014	Dec. 28, 2013
Continuous unrealized loss position, Fair Value
Fair value of available-for-sale securities, continuous loss position for less than twelve months	$ 32,086	$ 13,684
Fair value of available-for-sale securities, continuous loss position for twelve months or longer	11,505	10,632
Total fair value of available-for-sale securities, continuous loss position	43,591	24,316
Continuous unrealized loss position, Gross Unrealized Losses
Available-for-sale securities, continuous loss position for less than 12 months, gross unrealized losses	(44)	(15)
Available-for-sale securities, continuous loss position for 12 months or greater, gross unrealized losses	(920)	(1,793)
Available-for-sale securities, total gross unrealized losses	(964)	(1,808)
Cost
Due in one year or less, Cost	155,375
Due after one year through ten years, Cost	97,195
Due after ten years, Cost	25,005
Total Cost	277,575
Fair Value
Due in one year or less, Fair Value	155,485
Due after one year through ten years, Fair Value	97,329
Due after ten years, Fair Value	24,085
Total Fair Value	276,899
Corporate bonds
Continuous unrealized loss position, Fair Value
Fair value of available-for-sale securities, continuous loss position for less than twelve months	16,564	2,605
Total fair value of available-for-sale securities, continuous loss position	16,564	2,605
Continuous unrealized loss position, Gross Unrealized Losses
Available-for-sale securities, continuous loss position for less than 12 months, gross unrealized losses	(33)	(4)
Available-for-sale securities, total gross unrealized losses	(33)	(4)
Auction rate securities
Continuous unrealized loss position, Fair Value
Fair value of available-for-sale securities, continuous loss position for twelve months or longer	11,505	10,632
Total fair value of available-for-sale securities, continuous loss position	11,505	10,632
Continuous unrealized loss position, Gross Unrealized Losses
Available-for-sale securities, continuous loss position for 12 months or greater, gross unrealized losses	(920)	(1,793)
Available-for-sale securities, total gross unrealized losses	(920)	(1,793)
Municipal bonds
Continuous unrealized loss position, Fair Value
Fair value of available-for-sale securities, continuous loss position for less than twelve months	7,893	11,079
Total fair value of available-for-sale securities, continuous loss position	7,893	11,079
Continuous unrealized loss position, Gross Unrealized Losses
Available-for-sale securities, continuous loss position for less than 12 months, gross unrealized losses	(3)	(11)
Available-for-sale securities, total gross unrealized losses	(3)	(11)
Asset-backed securities
Continuous unrealized loss position, Fair Value
Fair value of available-for-sale securities, continuous loss position for less than twelve months	5,102
Total fair value of available-for-sale securities, continuous loss position	5,102
Continuous unrealized loss position, Gross Unrealized Losses
Available-for-sale securities, continuous loss position for less than 12 months, gross unrealized losses	(3)
Available-for-sale securities, total gross unrealized losses	(3)
International government bonds
Continuous unrealized loss position, Fair Value
Fair value of available-for-sale securities, continuous loss position for less than twelve months	2,527
Total fair value of available-for-sale securities, continuous loss position	2,527
Continuous unrealized loss position, Gross Unrealized Losses
Available-for-sale securities, continuous loss position for less than 12 months, gross unrealized losses	(5)
Available-for-sale securities, total gross unrealized losses	$ (5)