Business Segments - Revenue Information by Geographic Region (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 28, 2019	Sep. 29, 2018	Sep. 28, 2019	Sep. 29, 2018
Revenues From External Customers And Long Lived Assets [Line Items]
Total revenues	$ 10,664	$ 11,320	$ 31,685	$ 31,133
United States
Revenues From External Customers And Long Lived Assets [Line Items]
Total revenues	5,833	6,182	16,362	16,156
Europe
Revenues From External Customers And Long Lived Assets [Line Items]
Total revenues	2,112	2,020	7,176	6,680
Rest of Americas
Revenues From External Customers And Long Lived Assets [Line Items]
Total revenues	735	554	2,107	1,862
Asia/Pacific Rim
Revenues From External Customers And Long Lived Assets [Line Items]
Total revenues	$ 1,984	$ 2,564	$ 6,040	$ 6,435