Business Segments - Revenue Information by Geographic Region (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 27, 2020	Jun. 29, 2019	Jun. 27, 2020	Jun. 29, 2019
Revenues From External Customers And Long Lived Assets [Line Items]
Total revenues	$ 6,219	$ 10,426	$ 15,240	$ 21,021
United States
Revenues From External Customers And Long Lived Assets [Line Items]
Total revenues	3,171	5,327	7,612	10,529
Europe
Revenues From External Customers And Long Lived Assets [Line Items]
Total revenues	1,419	2,587	3,403	5,064
Rest of Americas
Revenues From External Customers And Long Lived Assets [Line Items]
Total revenues	219	754	622	1,372
Asia/Pacific Rim
Revenues From External Customers And Long Lived Assets [Line Items]
Total revenues	$ 1,410	$ 1,758	$ 3,603	$ 4,056