Segment Information (Long-Lived Assets by Geographic Region) (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	$ 19,735	$ 17,245
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	11,823	12,236
Europe
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	6,761	3,437
Rest of the World
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	$ 1,151	$ 1,572