Segment Information - Summary of Revenue by Product Type (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Product Information [Line Items]
Total revenue	$ 3,535	$ 7,106	$ 7,822	$ 16,016
Core [Member]
Product Information [Line Items]
Total revenue	689	4,029	1,158	9,138
Wafer [Member]
Product Information [Line Items]
Total revenue	1,830	1,742	4,175	3,633
Optical [Member]
Product Information [Line Items]
Total revenue	904	1,191	2,280	2,959
Research & Development [Member]
Product Information [Line Items]
Total revenue	$ 112	$ 144	$ 209	$ 286