CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	3 Months Ended
	Mar. 28, 2020	Mar. 30, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (1,224)	$ (2,392)
Other comprehensive income, before tax:
Change in unrealized net gain (loss) on available-for-sale investments	2	45
Foreign currency translation gains and (losses)	(95)	61
Other comprehensive income (loss), before tax	(93)	106
Income tax provision related to items in other comprehensive income	0	0
Other comprehensive income (loss), net of tax	(93)	106
Comprehensive loss	$ (1,317)	$ (2,286)