Investments - Marketable Debt Securities (Details) (USD $)	3 Months Ended
	Mar. 29, 2014	Mar. 30, 2013	Dec. 28, 2013
Schedule of Available-for-sale Securities [Line Items]
Proceeds from maturity of marketable debt securities	$ 10,000,000	$ 5,800,000
Investments of marketable debt securities [Abstract]
Amortized cost	82,578,000		86,770,000
Unrealized gains	59,000		51,000
Unrealized losses	(21,000)		(30,000)
Fair value	82,616,000		86,791,000
Amortized Cost [Abstract]
Marketable debt securities - current (due in less than one year)	52,112,000		52,122,000
Marketable debt securities - non-current (due in one to two years)	30,466,000		34,648,000
Marketable debt securities Total Amortized Cost	82,578,000		86,770,000
Fair Value [Abstract]
Marketable debt securities - current (due in less than one year)	52,147,000		52,159,000
Marketable debt securities - non-current (due in one to two years)	30,469,000		34,632,000
Marketable Debt Securities Total Fair value	82,616,000		86,791,000
U.S. Treasury securities [Member]
Investments of marketable debt securities [Abstract]
Amortized cost	23,979,000		23,975,000
Unrealized gains	19,000		15,000
Unrealized losses	0		(1,000)
Fair value	23,998,000		23,989,000
Corporate bonds [Member]
Investments of marketable debt securities [Abstract]
Amortized cost	30,669,000		35,804,000
Unrealized gains	5,000		3,000
Unrealized losses	(15,000)		(23,000)
Fair value	30,659,000		35,784,000
U.S. Agency bonds [Member]
Investments of marketable debt securities [Abstract]
Amortized cost	19,516,000		19,517,000
Unrealized gains	10,000		10,000
Unrealized losses	(6,000)		(4,000)
Fair value	19,520,000		19,523,000
Municipal bonds [Member]
Investments of marketable debt securities [Abstract]
Amortized cost	8,414,000		7,474,000
Unrealized gains	25,000		23,000
Unrealized losses	0		(2,000)
Fair value	$ 8,439,000		$ 7,495,000