Segment Information (Long-Lived Assets by Geographic Region) (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	$ 17,530	$ 19,049
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	12,274	13,052
Europe
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	3,555	3,920
Republic of Korea
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	105	168
Rest of the World
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	$ 1,596	$ 1,909