Segment Information - Summary of Revenue by Product Type (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Product Information [Line Items]
Revenue	$ 10,555	$ 17,003	$ 18,862	$ 27,210
Operating Segments [Member] | Core [Member]
Product Information [Line Items]
Revenue	5,979	5,315	6,966	8,073
Operating Segments [Member] | Polished [Member]
Product Information [Line Items]
Revenue	3,312	10,448	9,369	16,129
Operating Segments [Member] | Optical [Member]
Product Information [Line Items]
Revenue	1,151	1,208	2,293	2,967
Operating Segments [Member] | Other [Member]
Product Information [Line Items]
Revenue	$ 113	$ 32	$ 234	$ 41