Changes in Accumulated Other Comprehensive Income by Component (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jul. 01, 2017	Jun. 30, 2018	Jul. 01, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassification	$ (122)	$ 40	$ (46)	$ 78
Amounts reclassified from other comprehensive income	0	0	0	0
Other comprehensive income (loss), net of tax	(122)	40	(46)	78
Ending balance	78,586		78,586
Foreign currency
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	639	377	535	343
Other comprehensive income (loss) before reclassification	(144)	41	(40)	75
Amounts reclassified from other comprehensive income	0	0	0	0
Other comprehensive income (loss), net of tax	(144)	41	(40)	75
Ending balance	495	418	495	418
Unrealized holding losses on available-for-sale investments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(73)	(18)	(45)	(22)
Other comprehensive income (loss) before reclassification	22	(1)	(6)	3
Amounts reclassified from other comprehensive income	0	0	0	0
Other comprehensive income (loss), net of tax	22	(1)	(6)	3
Ending balance	(51)	(19)	(51)	(19)
Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	566	359	490	321
Amounts reclassified from other comprehensive income	0	0	0	0
Ending balance	$ 444	$ 399	$ 444	$ 399