Equity - Changes in Accumulated Other Comprehensive Income by Component (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 27, 2020	Jun. 29, 2019	Jun. 27, 2020	Jun. 29, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ 95,669	$ 89,087	$ 95,793	$ 89,624
Other comprehensive income (loss), net of tax	71	(29)	(22)	77
Ending balance	97,655	88,347	97,655	88,347
Foreign currency
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	286	466	381	405
Other comprehensive income (loss) before reclassification	20	(61)	(75)	0
Other comprehensive income (loss), net of tax	20	(61)	(75)	0
Ending balance	306	405	306	405
Unrealized holding gains (losses) on available- for-sale investments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	45	18	43	(27)
Other comprehensive income (loss) before reclassification	51	32	53	77
Other comprehensive income (loss), net of tax	51	32	53	77
Ending balance	96	50	96	50
Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	331	484	424	378
Other comprehensive income (loss) before reclassification	71	(29)	(22)	77
Other comprehensive income (loss), net of tax	71	(29)	(22)	77
Ending balance	$ 402	$ 455	$ 402	$ 455