Cash, Cash Equivalents and Investments (Details 2) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Jan. 01, 2011
Continuous unrealized loss position, Fair Value
Fair value of available-for-sale securities, continuous loss position for less than twelve months	$ 46,186	$ 58,386
Fair value of available-for-sale securities, continuous loss position for twelve month or longer	17,477	18,798
Total fair value of available-for-sale securities, continuous loss position	63,663	77,184
Continuous unrealized loss position, Gross Unrealized Losses
Available-for-sale securities, continuous loss position for less than 12 months, gross unrealized losses	(392)	(69)
Available-for-sale securities, continuous loss position for 12 months or greater, gross unrealized losses	(1,748)	(2,227)
Available-for-sale securities, total gross unrealized losses	(2,140)	(2,296)
Cost
Due in one year or less, Cost	148,641
Due after one year through ten years, Cost	78,254
Due after ten years, Cost	55,755
Total Cost	282,650
Fair Value
Due in one year or less, Fair Value	148,734
Due after one year through ten years, Fair Value	78,113
Due after ten years, Fair Value	54,007
Total Fair Value	280,854
Municipal bonds
Continuous unrealized loss position, Fair Value
Fair value of available-for-sale securities, continuous loss position for less than twelve months	10,437	22,272
Total fair value of available-for-sale securities, continuous loss position	10,437	22,272
Continuous unrealized loss position, Gross Unrealized Losses
Available-for-sale securities, continuous loss position for less than 12 months, gross unrealized losses	(12)	(18)
Available-for-sale securities, total gross unrealized losses	(12)	(18)
Auction rate securities
Continuous unrealized loss position, Fair Value
Fair value of available-for-sale securities, continuous loss position for twelve month or longer	17,477	17,500
Total fair value of available-for-sale securities, continuous loss position	17,477	17,500
Continuous unrealized loss position, Gross Unrealized Losses
Available-for-sale securities, continuous loss position for 12 months or greater, gross unrealized losses	(1,748)	(2,225)
Available-for-sale securities, total gross unrealized losses	(1,748)	(2,225)
U.S. government agency
Continuous unrealized loss position, Fair Value
Fair value of available-for-sale securities, continuous loss position for less than twelve months	5,772	17,007
Total fair value of available-for-sale securities, continuous loss position	5,772	17,007
Continuous unrealized loss position, Gross Unrealized Losses
Available-for-sale securities, continuous loss position for less than 12 months, gross unrealized losses	(12)	(5)
Available-for-sale securities, total gross unrealized losses	(12)	(5)
Asset-backed securities
Continuous unrealized loss position, Fair Value
Fair value of available-for-sale securities, continuous loss position for less than twelve months	4,539
Total fair value of available-for-sale securities, continuous loss position	4,539
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)
Corporate bonds
Continuous unrealized loss position, Fair Value
Fair value of available-for-sale securities, continuous loss position for less than twelve months	25,438	17,538
Fair value of available-for-sale securities, continuous loss position for twelve month or longer		1,298
Total fair value of available-for-sale securities, continuous loss position	25,438	18,836
Continuous unrealized loss position, Gross Unrealized Losses
Available-for-sale securities, continuous loss position for less than 12 months, gross unrealized losses	(363)	(44)
Available-for-sale securities, continuous loss position for 12 months or greater, gross unrealized losses		(2)
Available-for-sale securities, total gross unrealized losses	(363)	(46)
Certificates of deposit
Continuous unrealized loss position, Fair Value
Fair value of available-for-sale securities, continuous loss position for less than twelve months		1,569
Total fair value of available-for-sale securities, continuous loss position		1,569
Continuous unrealized loss position, Gross Unrealized Losses
Available-for-sale securities, continuous loss position for less than 12 months, gross unrealized losses		(2)
Available-for-sale securities, total gross unrealized losses		$ (2)