Condensed Consolidated Statements of Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 26, 2020	Sep. 28, 2019	Sep. 26, 2020	Sep. 28, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (1,719)	$ (1,785)	$ (6,150)	$ (7,252)
Foreign currency translation adjustments	(41)	36	(48)	32
Comprehensive loss	$ (1,760)	$ (1,749)	$ (6,198)	$ (7,220)