Marketable Debt Securities (Details) (USD $)	3 Months Ended
	Mar. 30, 2013		Dec. 29, 2012
Schedule of Available-for-sale Securities [Line Items]
ProceedsFromSaleAndMaturityOfAvailableForSaleSecuritesNet	$ 5,800,000
Investments of marketable debt securities [Abstract]
Amortized cost	96,535,000		89,873,000
Unrealized Gains	44,000		57,000
Unrealized Losses	(23,000)		(24,000)
Marketable debt securities	96,556,000	[1]	89,906,000	[1]
Amortized Cost [Abstract]
Marketable debt securities - current (due in less than one year)	57,851,000		51,238,000
Marketable debt securities - non-current (due in one to two years)	38,684,000		38,635,000
Marketable debt securities	96,535,000		89,873,000
Fair Value [Abstract]
Marketable debt securities - current (due in less than one year)	57,856,000	[1]	51,264,000	[1]
Marketable debt securities - non-current (due in one to two years)	38,700,000	[1]	38,642,000	[1]
Marketable debt securities	96,556,000	[1]	89,906,000	[1]
U.S. Treasury securities [Member]
Investments of marketable debt securities [Abstract]
Amortized cost	32,510,000		32,518,000
Unrealized Gains	22,000		24,000
Unrealized Losses	0		0
Marketable debt securities	32,532,000	[1]	32,542,000	[1]
Corporate bonds [Member]
Investments of marketable debt securities [Abstract]
Amortized cost	38,224,000		31,929,000
Unrealized Gains	7,000		2,000
Unrealized Losses	(20,000)		(23,000)
Marketable debt securities	38,211,000	[1]	31,908,000	[1]
Agency Securities [Member]
Investments of marketable debt securities [Abstract]
Amortized cost	20,088,000		17,632,000
Unrealized Gains	12,000		11,000
Unrealized Losses	(2,000)		(1,000)
Marketable debt securities	20,098,000	[1]	17,642,000	[1]
Municipal bonds [Member]
Investments of marketable debt securities [Abstract]
Amortized cost	5,713,000		7,794,000
Unrealized Gains	3,000		20,000
Unrealized Losses	(1,000)		0
Marketable debt securities	$ 5,715,000	[1]	$ 7,814,000	[1]

[1] See Note 2 for discussion of fair value measurements.