Segment Information - Summary of Revenue by Product Type (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Product Information [Line Items]
Total Revenue	$ 7,106	$ 14,469	$ 16,016	$ 28,737
Core [Member]
Product Information [Line Items]
Total Revenue	4,029	9,572	9,138	20,927
Wafer [Member]
Product Information [Line Items]
Total Revenue	1,742	2,860	3,633	4,010
Optical [Member]
Product Information [Line Items]
Total Revenue	1,191	1,765	2,959	3,403
Research & Development [Member]
Product Information [Line Items]
Total Revenue	$ 144	$ 272	$ 286	$ 397