Segment Information - Summary of Revenue by Product Type (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Product Information [Line Items]
Revenue	$ 8,910	$ 14,268
Core [Member]
Product Information [Line Items]
Revenue	5,109	11,355
Wafer [Member]
Product Information [Line Items]
Revenue	1,891	1,095
Optical [Member]
Product Information [Line Items]
Revenue	1,769	1,638
Research & Development [Member]
Product Information [Line Items]
Revenue	141	125
Other Product [Member]
Product Information [Line Items]
Revenue		$ 55