Changes in Accumulated Other Comprehensive Income by Component (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 29, 2018	Sep. 30, 2017	Sep. 29, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ 78,586	$ 78,107	$ 82,663	$ 73,266
Other comprehensive income (loss) before reclassification	(73)	44	(119)	122
Amounts reclassified from other comprehensive income	0	0	0	0
Other comprehensive income (loss), net of tax	(73)	44	(119)	122
Ending balance	79,342	81,418	79,342	81,418
Foreign currency
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	495	418	535	343
Other comprehensive income (loss) before reclassification	(86)	39	(126)	114
Amounts reclassified from other comprehensive income	0	0	0	0
Other comprehensive income (loss), net of tax	(86)	39	(126)	114
Ending balance	409	457	409	457
Unrealized holding losses on available-for-sale investments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(51)	(19)	(45)	(22)
Other comprehensive income (loss) before reclassification	13	5	7	8
Amounts reclassified from other comprehensive income	0	0	0	0
Other comprehensive income (loss), net of tax	13	5	7	8
Ending balance	(38)	(14)	(38)	(14)
Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	444	399	490	321
Amounts reclassified from other comprehensive income	0	0	0	0
Ending balance	$ 371	$ 443	$ 371	$ 443