Fair Value of Financial Instruments - Available- for-sale investment (Details) - USD ($) $ in Thousands	6 Months Ended
	Jul. 02, 2016	Jan. 02, 2016
Cost
Due in one year or less, Cost	$ 104,001
Due after one year through ten years, Cost	55,269
Due after ten years, Cost	25,530
Total Cost	184,800
Fair Value
Due in one year or less, Fair Value	104,037
Due after one year through ten years, Fair Value	55,387
Due after ten years, Fair Value	24,451
Total Fair Value	183,875
Continuous unrealized loss position, Fair Value
Fair value of available-for-sale securities, continuous loss position for less than twelve months	16,335	$ 32,487
Fair value of available-for-sale securities, continuous loss position for twelve months or longer	8,426	8,324
Total fair value of available-for-sale securities, continuous loss position	24,761	40,811
Continuous unrealized loss position, Gross Unrealized Losses
Available-for-sale securities, continuous loss position for less than 12 months, gross unrealized losses	(10)	(40)
Available-for-sale securities, continuous loss position for 12 months or greater, gross unrealized losses	(1,080)	(876)
Available-for-sale securities, total gross unrealized losses	(1,090)	(916)
Other than temporary impairment losses
Other-than-temporary impairment losses	0
Available for sale unrealized gains	0	0
Municipal bonds
Continuous unrealized loss position, Fair Value
Fair value of available-for-sale securities, continuous loss position for less than twelve months	11,276	29,271
Fair value of available-for-sale securities, continuous loss position for twelve months or longer	1,505	1,198
Total fair value of available-for-sale securities, continuous loss position	12,781	30,469
Continuous unrealized loss position, Gross Unrealized Losses
Available-for-sale securities, continuous loss position for less than 12 months, gross unrealized losses	(4)	(30)
Available-for-sale securities, continuous loss position for 12 months or greater, gross unrealized losses	(1)	(2)
Available-for-sale securities, total gross unrealized losses	(5)	(32)
Auction rate securities
Continuous unrealized loss position, Fair Value
Fair value of available-for-sale securities, continuous loss position for twelve months or longer	6,921	7,126
Total fair value of available-for-sale securities, continuous loss position	6,921	7,126
Continuous unrealized loss position, Gross Unrealized Losses
Available-for-sale securities, continuous loss position for 12 months or greater, gross unrealized losses	(1,079)	(874)
Available-for-sale securities, total gross unrealized losses	(1,079)	(874)
International government bonds
Continuous unrealized loss position, Fair Value
Fair value of available-for-sale securities, continuous loss position for less than twelve months		2,220
Total fair value of available-for-sale securities, continuous loss position		2,220
Continuous unrealized loss position, Gross Unrealized Losses
Available-for-sale securities, continuous loss position for less than 12 months, gross unrealized losses		(7)
Available-for-sale securities, total gross unrealized losses		(7)
Corporate bonds
Continuous unrealized loss position, Fair Value
Fair value of available-for-sale securities, continuous loss position for less than twelve months	5,059	996
Total fair value of available-for-sale securities, continuous loss position	5,059	996
Continuous unrealized loss position, Gross Unrealized Losses
Available-for-sale securities, continuous loss position for less than 12 months, gross unrealized losses	(6)	(3)
Available-for-sale securities, total gross unrealized losses	$ (6)	$ (3)