Segment Information (Long-Lived Assets by Geographic Region) (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	$ 17,245	$ 19,049
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	12,236	13,052
Europe
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	3,437	3,920
Rest of the World
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	$ 1,572	$ 2,077