Business Segments - Revenue Information by Geographic Region (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 26, 2020	Sep. 28, 2019	Sep. 26, 2020	Sep. 28, 2019
Revenues From External Customers And Long Lived Assets [Line Items]
Total revenues	$ 8,803	$ 10,664	$ 24,043	$ 31,685
United States
Revenues From External Customers And Long Lived Assets [Line Items]
Total revenues	5,269	5,833	12,881	16,362
Europe
Revenues From External Customers And Long Lived Assets [Line Items]
Total revenues	1,913	2,112	5,316	7,176
Rest of Americas
Revenues From External Customers And Long Lived Assets [Line Items]
Total revenues	599	735	1,221	2,107
Asia/Pacific Rim
Revenues From External Customers And Long Lived Assets [Line Items]
Total revenues	$ 1,022	$ 1,984	$ 4,625	$ 6,040