Marketable Debt Securities (Details) (USD $)	3 Months Ended			9 Months Ended
	Sep. 28, 2013		Sep. 29, 2012	Sep. 28, 2013		Sep. 29, 2012	Dec. 29, 2012
Schedule of Available-for-sale Securities [Line Items]
Proceeds from maturity of marketable debt securities	$ 8,500,000		$ 0	$ 31,800,000		$ 10,000,000
Investments of marketable debt securities [Abstract]
Amortized cost	83,053,000			83,053,000			89,873,000
Unrealized gains	64,000			64,000			57,000
Unrealized losses	(27,000)			(27,000)			(24,000)
Fair value	83,090,000	[1]		83,090,000	[1]		89,906,000	[1]
Amortized Cost [Abstract]
Marketable debt securities - current (due in less than one year)	57,371,000			57,371,000			51,238,000
Marketable debt securities - non-current (due in one to two years)	25,682,000			25,682,000			38,635,000
Marketable debt securities	83,053,000			83,053,000			89,873,000
Fair Value [Abstract]
Marketable debt securities - current (due in less than one year)	57,407,000	[1]		57,407,000	[1]		51,264,000	[1]
Marketable debt securities - non-current (due in one to two years)	25,683,000	[1]		25,683,000	[1]		38,642,000	[1]
U.S. Treasury securities [Member]
Investments of marketable debt securities [Abstract]
Amortized cost	23,998,000			23,998,000			32,518,000
Unrealized gains	24,000			24,000			24,000
Unrealized losses	0			0			0
Fair value	24,022,000	[1]		24,022,000	[1]		32,542,000	[1]
Corporate bonds [Member]
Investments of marketable debt securities [Abstract]
Amortized cost	33,100,000			33,100,000			31,929,000
Unrealized gains	5,000			5,000			2,000
Unrealized losses	(22,000)			(22,000)			(23,000)
Fair value	33,083,000	[1]		33,083,000	[1]		31,908,000	[1]
U.S. Agency bonds [Member]
Investments of marketable debt securities [Abstract]
Amortized cost	17,528,000			17,528,000			17,632,000
Unrealized gains	12,000			12,000			11,000
Unrealized losses	(1,000)			(1,000)			(1,000)
Fair value	17,539,000	[1]		17,539,000	[1]		17,642,000	[1]
Municipal bonds [Member]
Investments of marketable debt securities [Abstract]
Amortized cost	8,427,000			8,427,000			7,794,000
Unrealized gains	23,000			23,000			20,000
Unrealized losses	(4,000)			(4,000)			0
Fair value	$ 8,446,000	[1]		$ 8,446,000	[1]		$ 7,814,000	[1]

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