Segment Information - Summary of Revenue by Product Type (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Product Information [Line Items]
Total revenue	$ 7,086	$ 5,346	$ 14,908	$ 21,362
Core [Member]
Product Information [Line Items]
Total revenue	424	1,824	1,514	10,962
Wafer [Member]
Product Information [Line Items]
Total revenue	5,507	2,136	9,683	5,769
Optical [Member]
Product Information [Line Items]
Total revenue	1,075	1,116	3,422	4,075
Research & Development [Member]
Product Information [Line Items]
Total revenue	$ 80	$ 270	$ 289	$ 556