Basis of Presentation and General Information (Narrative) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 27, 2019	Sep. 28, 2018	Sep. 27, 2019	Sep. 28, 2018	Dec. 29, 2018	Dec. 28, 2018	Dec. 29, 2017
Basis Of Presentation And General Information [Line Items]
Revenue recognized as a result of change in contract liability	$ 3,800,000	$ 4,200,000	$ 12,000,000	$ 14,000,000
Deferred commissions						$ 1,200,000	$ 1,400,000
Commissions expense	400,000	100,000	900,000	700,000
Impairment loss recognized to capitalization of deferred commission	0	$ 0	0	$ 0
Additional operating liabilities	8,293,000		8,293,000		$ 9,000,000
Additional operating ROU	$ 8,293,000		$ 8,293,000		$ 9,000,000
Minimum [Member]
Basis Of Presentation And General Information [Line Items]
Business relationship agreement period			6 months
Maximum [Member]
Basis Of Presentation And General Information [Line Items]
Business relationship agreement period			12 months
Customer contract period			12 months