Business Segments - Revenue Information by Geographic Region (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jul. 01, 2017	Jun. 30, 2018	Jul. 01, 2017
Revenues From External Customers And Long Lived Assets [Line Items]
Total revenues	$ 10,304	$ 10,002	$ 19,813	$ 20,485
United States
Revenues From External Customers And Long Lived Assets [Line Items]
Total revenues	5,114	5,882	9,974	11,586
Europe
Revenues From External Customers And Long Lived Assets [Line Items]
Total revenues	2,226	1,840	4,660	3,775
Rest of Americas
Revenues From External Customers And Long Lived Assets [Line Items]
Total revenues	656	555	1,308	1,164
Asia/Pacific Rim
Revenues From External Customers And Long Lived Assets [Line Items]
Total revenues	$ 2,308	$ 1,725	$ 3,871	$ 3,960