Information about Operating Segments and Geographic Areas - Revenue and Long-Lived Assets by Geographic Area (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Total revenue:
Total revenue	$ 16,839	$ 16,694	$ 19,203	$ 20,678	$ 19,469	$ 19,653	$ 18,848	$ 22,841	$ 73,414	$ 80,811
Long-lived assets:
Total long-lived assets	5,692				5,181				5,692	5,181
North America [Member]
Total revenue:
Total revenue									69,088	76,062
Long-lived assets:
Total long-lived assets	1,578				991				1,578	991
Asia [Member]
Total revenue:
Total revenue									1,271	1,644
Long-lived assets:
Total long-lived assets	91				76				91	76
Europe [Member]
Total revenue:
Total revenue									3,055	3,105
Long-lived assets:
Total long-lived assets	$ 4,023				$ 4,114				$ 4,023	$ 4,114