Information about Geographic Areas and Operating Segments - Total Revenue and Long-Lived Assets by Geographic Area (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Total revenue:
Total revenue	$ 16,694	$ 19,653	$ 56,575	$ 61,342
Long-lived assets:
Total long-lived assets	5,539		5,539		$ 5,181
North America [Member]
Total revenue:
Total revenue	15,441	17,982	52,909	57,480
Long-lived assets:
Total long-lived assets	1,388		1,388		991
Asia [Member]
Total revenue:
Total revenue	579	875	1,164	1,429
Long-lived assets:
Total long-lived assets	100		100		76
Europe [Member]
Total revenue:
Total revenue	674	$ 796	2,502	$ 2,433
Long-lived assets:
Total long-lived assets	$ 4,051		$ 4,051		$ 4,114