Summary of Quarterly Financial Information (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Quarterly Financial Information [Line Items]
Product revenue	$ 10,528	$ 8,252	$ 9,224	$ 8,691	$ 9,896	$ 7,770	$ 6,753	$ 6,183	$ 36,695	$ 30,602	$ 21,677
Cost of product revenue	5,117	4,411	5,574	5,514	6,206	4,726	4,074	3,529	20,616	18,535	12,046
Gross profit on product revenue	5,411	3,841	3,650	3,177	3,690	3,044	2,679	2,654	16,079	12,067	9,631
Government grants and cooperative agreements revenue	0	0	0	91	527	1,479	0	436	91	2,442	1,432
Research and development	2,164	1,903	1,712	1,824	1,562	1,814	1,994	1,808	7,603	7,178	5,195
Selling, general and administrative	6,794	6,219	6,686	5,966	5,938	5,380	6,207	5,528	25,665	23,053	21,577
Amortization of intangible assets	51	50	51	50	50	51	51	50	202	202	67
Total operating expenses	9,009	8,172	8,449	7,840	7,550	7,245	8,252	7,386	33,470	30,433	27,021
Loss from operations	(3,598)	(4,331)	(4,799)	(4,572)	(3,333)	(2,722)	(5,573)	(4,296)	(17,300)	(15,924)	(15,958)
Total non-operating income (expense), net	1,993	926	2,933	(4,227)	(4,353)	5,026	(809)	(779)	1,625	(915)	(859)
Income (loss) before income taxes	(1,605)	(3,405)	(1,866)	(8,799)	(7,686)	2,304	(6,382)	(5,075)	(15,675)	(16,839)	(16,817)
Provision for income taxes	111	55	41	35	49	44	27	23	242	143	94
Net income (loss)	$ (1,716)	$ (3,460)	$ (1,907)	$ (8,834)	$ (7,735)	$ 2,260	$ (6,409)	$ (5,098)	$ (15,917)	$ (16,982)	$ (16,911)
Basic	$ (0.03)	$ (0.06)	$ (0.04)	$ (0.17)	$ (0.16)	$ 0.05	$ (0.13)	$ (0.11)	$ (0.29)	$ (0.35)	$ (0.42)
Diluted	$ (0.07)	$ (0.08)	$ (0.10)	$ (0.17)	$ (0.16)	$ 0.05	$ (0.13)	$ (0.11)	$ (0.33)	$ (0.35)	$ (0.42)