Investments - Marketable Debt Securities (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 04, 2015	Jun. 28, 2014	Jul. 04, 2015	Jun. 28, 2014	Jan. 03, 2015
Schedule of Available-for-sale Securities [Line Items]
Proceeds from Sale and Maturity of Available-for-sale Securities	$ 25,600	$ 13,500	$ 41,800	$ 23,500
Investments of marketable debt securities [Abstract]
Marketable debt securities Total Amortized Cost	91,101		91,101		$ 114,105
Unrealized gains	52		52		20
Unrealized losses	(23)		(23)		(75)
Fair value	91,130		91,130		114,050
Amortized Cost [Abstract]
Marketable debt securities - current (due in less than one year)	62,359		62,359		69,607
Marketable debt securities - non-current (due in one to two years)	28,742		28,742		44,498
Marketable debt securities Total Amortized Cost	91,101		91,101		114,105
Fair Value [Abstract]
Marketable debt securities - current (due in less than one year)	62,379		62,379		69,609
Marketable debt securities - non-current (due in one to two years)	28,751		28,751		44,441
Fair value	91,130		91,130		114,050
U.S. Treasury securities [Member]
Investments of marketable debt securities [Abstract]
Marketable debt securities Total Amortized Cost	22,503		22,503		32,507
Unrealized gains	24		24		12
Unrealized losses	0		0		(23)
Fair value	22,527		22,527		32,496
Amortized Cost [Abstract]
Marketable debt securities Total Amortized Cost	22,503		22,503		32,507
Fair Value [Abstract]
Fair value	22,527		22,527		32,496
Corporate bonds [Member]
Investments of marketable debt securities [Abstract]
Marketable debt securities Total Amortized Cost	27,700		27,700		35,409
Unrealized gains	3		3		2
Unrealized losses	(17)		(17)		(36)
Fair value	27,686		27,686		35,375
Amortized Cost [Abstract]
Marketable debt securities Total Amortized Cost	27,700		27,700		35,409
Fair Value [Abstract]
Fair value	27,686		27,686		35,375
U.S. Agency bonds [Member]
Investments of marketable debt securities [Abstract]
Marketable debt securities Total Amortized Cost	22,517		22,517		22,545
Unrealized gains	24		24		4
Unrealized losses	0		0		(10)
Fair value	22,541		22,541		22,539
Amortized Cost [Abstract]
Marketable debt securities Total Amortized Cost	22,517		22,517		22,545
Fair Value [Abstract]
Fair value	22,541		22,541		22,539
Commercial Paper, Not Included with Cash and Cash Equivalents [Member]
Investments of marketable debt securities [Abstract]
Marketable debt securities Total Amortized Cost	7,494		7,494		12,487
Unrealized gains	0		0		0
Unrealized losses	(1)		(1)		(1)
Fair value	7,493		7,493		12,486
Amortized Cost [Abstract]
Marketable debt securities Total Amortized Cost	7,494		7,494		12,487
Fair Value [Abstract]
Fair value	7,493		7,493		12,486
Municipal bonds [Member]
Investments of marketable debt securities [Abstract]
Marketable debt securities Total Amortized Cost	10,887		10,887		11,157
Unrealized gains	1		1		2
Unrealized losses	(5)		(5)		(5)
Fair value	10,883		10,883		11,154
Amortized Cost [Abstract]
Marketable debt securities Total Amortized Cost	10,887		10,887		11,157
Fair Value [Abstract]
Fair value	$ 10,883		$ 10,883		$ 11,154