Financial Statement Components - Components of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jul. 01, 2017	Jun. 30, 2018	Jul. 01, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance Value			$ 262,383
Current period change	$ (2,503)	$ 753	(605)	$ 2,689
Ending Balance Value	278,484		278,484
Foreign Currency Translations [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance Value			(1,647)
Current period change			(568)
Ending Balance Value	(2,215)		(2,215)
Defined Benefit Pension Plans [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance Value			(387)
Ending Balance Value	(387)		(387)
Unrealized Income (Loss) on Investment [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance Value			(90)
Current period change			(37)
Ending Balance Value	(127)		(127)
Accumulated Other Comprehensive Income (Loss) [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance Value			(2,124)
Current period change			(605)
Ending Balance Value	$ (2,729)		$ (2,729)