Revenues Based on Customer Location (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Segment Reporting Information [Line Items]
Total revenues	$ 21,287	$ 16,508
United States
Segment Reporting Information [Line Items]
Total revenues	1,303	1,760
Europe and Middle East
Segment Reporting Information [Line Items]
Total revenues	3,931	2,474
Asia Pacific
Segment Reporting Information [Line Items]
Total revenues	16,053	12,274
China
Segment Reporting Information [Line Items]
Total revenues	9,742	8,892
S. Korea
Segment Reporting Information [Line Items]
Total revenues	$ 3,749	$ 2,703