CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 27, 2020	Jun. 29, 2019	Jun. 27, 2020	Jun. 29, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net income (loss)	$ 1,524	$ (1,182)	$ 300	$ (3,574)
Other comprehensive income (loss), before tax:
Change in unrealized net gain on available-for-sale investments	51	32	53	77
Foreign currency translation gains (losses)	20	(61)	(75)	0
Other comprehensive income (loss), before tax	71	(29)	(22)	77
Income taxes related to items in other comprehensive income (loss)	0	0	0	0
Other comprehensive income (loss), net of tax	71	(29)	(22)	77
Comprehensive income (loss)	$ 1,595	$ (1,211)	$ 278	$ (3,497)