Business Segment, Geographic and Major Customer Information - Geographic Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	$ 34,692	$ 39,546	$ 77,949	$ 80,615
U.S.
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	31,114	36,176	69,990	72,886
Other countries
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	$ 3,578	$ 3,370	$ 7,959	$ 7,729