Cash, Cash Equivalents and Investments (Details) (USD $)	12 Months Ended
	Dec. 28, 2013	Dec. 29, 2012
Cash, Cash Equivalents and Investments
Auction-rate securities guaranteed by the U.S. government	$ 10,400,000
Auction-rate securities privately insured	2,000,000
Auction-rate securities having credit rating 'AA'	6,000,000
Auction-rate securities having credit rating 'A'	2,000,000
Auction-rate securities having credit rating 'BBB'	4,400,000
Other-than-temporary impairment losses	0
Cash on hand, Cost	45,544,000	56,690,000
Cash on hand, Fair Value	45,544,000	56,690,000
Cash and cash equivalents, Cost	95,800,000	105,424,000
Cash and cash equivalents, Gross Unrealized Gains		2,000
Cash and cash equivalents, Fair Value	95,800,000	105,426,000
Cash Equivalents:
Available-for-sale securities
Available-for-sale securities, Cost	50,256,000	48,734,000
Available-for-sale securities, Gross Unrealized Gains		2,000
Available-for-sale securities, Fair Value	50,256,000	48,736,000
Short-term Investments:
Available-for-sale securities
Available-for-sale securities, Cost	179,365,000	176,207,000
Available-for-sale securities, Gross Unrealized Losses	(15,000)	(12,000)
Available-for-sale securities, Gross Unrealized Gains	243,000	370,000
Available-for-sale securities, Fair Value	179,593,000	176,565,000
Long-term Investments:
Available-for-sale securities
Available-for-sale securities, Cost	12,425,000	12,525,000
Available-for-sale securities, Gross Unrealized Losses	(1,793,000)	(1,156,000)
Available-for-sale securities, Fair Value	10,632,000	11,369,000
U.S. Treasury bills | Cash Equivalents:
Available-for-sale securities
Available-for-sale securities, Cost		25,049,000
Available-for-sale securities, Gross Unrealized Gains		1,000
Available-for-sale securities, Fair Value		25,050,000
Money market funds | Cash Equivalents:
Available-for-sale securities
Available-for-sale securities, Cost	39,538,000	22,685,000
Available-for-sale securities, Gross Unrealized Gains		1,000
Available-for-sale securities, Fair Value	39,538,000	22,686,000
Certificates of deposit | Cash Equivalents:
Available-for-sale securities
Available-for-sale securities, Cost	7,768,000
Available-for-sale securities, Fair Value	7,768,000
Commercial paper | Cash Equivalents:
Available-for-sale securities
Available-for-sale securities, Cost	2,499,000
Available-for-sale securities, Fair Value	2,499,000
Commercial paper | Short-term Investments:
Available-for-sale securities
Available-for-sale securities, Cost	3,748,000
Available-for-sale securities, Fair Value	3,748,000
Municipal bonds | Cash Equivalents:
Available-for-sale securities
Available-for-sale securities, Cost	451,000	1,000,000
Available-for-sale securities, Fair Value	451,000	1,000,000
Municipal bonds | Short-term Investments:
Available-for-sale securities
Available-for-sale securities, Cost	119,289,000	45,646,000
Available-for-sale securities, Gross Unrealized Losses	(11,000)	(7,000)
Available-for-sale securities, Gross Unrealized Gains	182,000	50,000
Available-for-sale securities, Fair Value	119,460,000	45,689,000
Corporate bonds | Short-term Investments:
Available-for-sale securities
Available-for-sale securities, Cost	17,788,000	59,089,000
Available-for-sale securities, Gross Unrealized Losses	(4,000)	(5,000)
Available-for-sale securities, Gross Unrealized Gains	60,000	267,000
Available-for-sale securities, Fair Value	17,844,000	59,351,000
Variable-rate demand notes | Short-term Investments:
Available-for-sale securities
Available-for-sale securities, Cost	38,025,000	41,785,000
Available-for-sale securities, Fair Value	38,025,000	41,785,000
Asset-backed securities | Short-term Investments:
Available-for-sale securities
Available-for-sale securities, Cost	515,000	15,058,000
Available-for-sale securities, Gross Unrealized Gains	1,000	11,000
Available-for-sale securities, Fair Value	516,000	15,069,000
U.S. government bonds | Short-term Investments:
Available-for-sale securities
Available-for-sale securities, Cost		12,638,000
Available-for-sale securities, Gross Unrealized Gains		25,000
Available-for-sale securities, Fair Value		12,663,000
International government bonds | Short-term Investments:
Available-for-sale securities
Available-for-sale securities, Cost		1,991,000
Available-for-sale securities, Gross Unrealized Gains		17,000
Available-for-sale securities, Fair Value		2,008,000
Auction rate securities | Long-term Investments:
Available-for-sale securities
Available-for-sale securities, Cost	12,425,000	12,525,000
Available-for-sale securities, Gross Unrealized Losses	(1,793,000)	(1,156,000)
Available-for-sale securities, Fair Value	$ 10,632,000	$ 11,369,000