Revenues Based on Customer Location (Detail) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016		Jun. 30, 2017		Jun. 30, 2016
Segment Reporting Information [Line Items]
Total revenues	$ 20,575	$ 17,103		$ 41,862		$ 33,611
United States
Segment Reporting Information [Line Items]
Total revenues	3,622	3,406		4,925		5,166
Europe and Middle East
Segment Reporting Information [Line Items]
Total revenues	2,253	2,032		6,184		4,506
Asia Pacific
Segment Reporting Information [Line Items]
Total revenues	14,700	11,665		30,753		23,939
China
Segment Reporting Information [Line Items]
Total revenues	6,078	7,099		15,820		15,991
S. Korea
Segment Reporting Information [Line Items]
Total revenues	5,027	3,734		8,776		6,437
Japan
Segment Reporting Information [Line Items]
Total revenues	$ 2,692	$ 0	[1]	$ 0	[1]	$ 0	[1]

[1] *) Less than 10%