Cash, Cash Equivalents and Investments (Details) (USD $)	3 Months Ended
	Mar. 29, 2014	Dec. 28, 2013
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	37,132,000	45,544,000
Cash on hand, Fair Value	37,132,000	45,544,000
Cash and cash equivalents, Cost	128,323,000	95,800,000
Cash and cash equivalents, Fair Value	128,323,000	95,800,000
Cash Equivalents:
Available-for-sale securities
Available-for-sale securities, Cost	91,191,000	50,256,000
Available-for-sale securities, Fair Value	91,191,000	50,256,000
Short-term Investments:
Available-for-sale securities
Available-for-sale securities, Cost	194,489,000	179,365,000
Available-for-sale securities, Gross Unrealized Losses	(27,000)	(15,000)
Available-for-sale securities, Gross Unrealized Gains	303,000	243,000
Available-for-sale securities, Fair Value	194,765,000	179,593,000
Long-term Investments:
Available-for-sale securities
Available-for-sale securities, Cost	12,425,000	12,425,000
Available-for-sale securities, Gross Unrealized Losses	(1,428,000)	(1,793,000)
Available-for-sale securities, Fair Value	10,997,000	10,632,000
Money market funds | Cash Equivalents:
Available-for-sale securities
Available-for-sale securities, Cost	85,070,000	39,538,000
Available-for-sale securities, Fair Value	85,070,000	39,538,000
Certificates of deposit | Cash Equivalents:
Available-for-sale securities
Available-for-sale securities, Cost	6,121,000	7,768,000
Available-for-sale securities, Fair Value	6,121,000	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
Available-for-sale securities, Fair Value		451,000
Municipal bonds | Short-term Investments:
Available-for-sale securities
Available-for-sale securities, Cost	133,965,000	119,289,000
Available-for-sale securities, Gross Unrealized Losses	(11,000)	(11,000)
Available-for-sale securities, Gross Unrealized Gains	238,000	182,000
Available-for-sale securities, Fair Value	134,192,000	119,460,000
Corporate bonds | Short-term Investments:
Available-for-sale securities
Available-for-sale securities, Cost	23,776,000	17,788,000
Available-for-sale securities, Gross Unrealized Losses	(15,000)	(4,000)
Available-for-sale securities, Gross Unrealized Gains	64,000	60,000
Available-for-sale securities, Fair Value	23,825,000	17,844,000
Variable-rate demand notes | Short-term Investments:
Available-for-sale securities
Available-for-sale securities, Cost	35,840,000	38,025,000
Available-for-sale securities, Fair Value	35,840,000	38,025,000
Asset-backed securities | Short-term Investments:
Available-for-sale securities
Available-for-sale securities, Cost	908,000	515,000
Available-for-sale securities, Gross Unrealized Losses	(1,000)
Available-for-sale securities, Gross Unrealized Gains	1,000	1,000
Available-for-sale securities, Fair Value	908,000	516,000
Auction rate securities | Long-term Investments:
Available-for-sale securities
Available-for-sale securities, Cost	12,425,000	12,425,000
Available-for-sale securities, Gross Unrealized Losses	(1,428,000)	(1,793,000)
Available-for-sale securities, Fair Value	$ 10,997,000	$ 10,632,000