Segment Information - Long Lived Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Long-lived assets	$ 1,149	$ 1,388
United States
Segment Reporting Information [Line Items]
Long-lived assets	648	763
Hong Kong
Segment Reporting Information [Line Items]
Long-lived assets	78	140
China
Segment Reporting Information [Line Items]
Long-lived assets	112	199
Other foreign countries
Segment Reporting Information [Line Items]
Long-lived assets	$ 311	$ 286