Business Segments - Revenue Information by Geographic Region (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Apr. 01, 2017
Revenues From External Customers And Long Lived Assets [Line Items]
Total revenues	$ 9,509	$ 10,483
United States
Revenues From External Customers And Long Lived Assets [Line Items]
Total revenues	4,860	5,704
Europe
Revenues From External Customers And Long Lived Assets [Line Items]
Total revenues	2,434	1,935
Rest of Americas
Revenues From External Customers And Long Lived Assets [Line Items]
Total revenues	652	609
Asia/Pacific Rim
Revenues From External Customers And Long Lived Assets [Line Items]
Total revenues	$ 1,563	$ 2,235