Revenues Based on Customer Location (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting Information [Line Items]
Total revenues	$ 24,044	$ 17,846	$ 65,906	$ 51,457
United States
Segment Reporting Information [Line Items]
Total revenues	1,237	2,144	6,162	7,310
Europe and Middle East
Segment Reporting Information [Line Items]
Total revenues	1,267	2,986	7,451	7,492
Asia Pacific
Segment Reporting Information [Line Items]
Total revenues	21,540	12,716	52,293	36,655
China
Segment Reporting Information [Line Items]
Total revenues	15,188	7,073	31,008	23,064
S. Korea
Segment Reporting Information [Line Items]
Total revenues	$ 5,076	$ 4,901	$ 13,852	$ 11,338