Segment Information - Summary of Revenue by Product Type (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Product Information [Line Items]
Revenue	$ 11,115	$ 19,942	$ 29,977	$ 47,152
Operating Segments [Member] | Core [Member]
Product Information [Line Items]
Revenue	7,111	1,344	14,077	9,417
Operating Segments [Member] | Polished [Member]
Product Information [Line Items]
Revenue	2,070	16,580	11,439	32,709
Operating Segments [Member] | Optical [Member]
Product Information [Line Items]
Revenue	1,040	1,558	3,332	4,525
Operating Segments [Member] | Research & Development [Member]
Product Information [Line Items]
Revenue	883	422	1,091	447
Operating Segments [Member] | Other [Member]
Product Information [Line Items]
Revenue	$ 11	$ 38	$ 38	$ 54