Selected Quarterly Financial Data (Unaudited) (Details) (USD $)	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
Selected quarterly financial data
Net sales	$ 32,115,957	$ 28,772,956	$ 28,222,443	$ 25,641,392	$ 21,329,792	$ 24,383,110	$ 21,198,055	$ 23,116,949	$ 114,752,748	$ 90,027,906	$ 86,930,019
Gross margin	19,167,932	16,803,011	16,502,373	15,241,259	6,976,273	13,103,609	12,240,492	12,208,863	67,714,575	44,529,237	45,366,875
Net income (loss)	$ 3,814,806	$ 3,676,871	$ 3,442,247	$ 3,803,818	$ (5,901,051)	$ 1,136,285	$ (2,294,832)	$ 19,732	$ 14,737,742	$ (7,039,866)	$ (4,384,435)
Basic net income (loss) per share	$ 0.07	$ 0.07	$ 0.06	$ 0.07	$ (0.11)	$ 0.02	$ (0.04)	$ 0.00	$ 0.27	$ (0.12)	$ (0.07)
Diluted net income (loss) per share	$ 0.07	$ 0.07	$ 0.06	$ 0.07	$ (0.11)	$ 0.02	$ (0.04)	$ 0.00	$ 0.27	$ (0.12)	$ (0.07)