17. Quarterly results of operations (unaudited) (Details) - Quarterly Financial Information 2012 (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Quarterly Financial Information 2012 [Abstract]
Net sales	$ 12,528	$ 16,768	$ 15,788	$ 15,057	$ 19,616	$ 15,358	$ 15,853	$ 17,559	$ 60,141	$ 68,386	$ 65,969
Gross profit	5,001	7,206	6,452	6,433	7,683	5,679	5,842	6,778	25,092	25,982	24,626
Net income	$ 1,109	$ 1,451	$ 1,215	$ 1,160	$ 1,882	$ 23	$ 508	$ 1,208	$ 4,935	$ 3,621	$ 4,676
Net income per share:
Basic (in Dollars per share)	$ 0.13	$ 0.17	$ 0.14	$ 0.13	$ 0.21	$ 0.00	$ 0.06	$ 0.13	$ 0.57	$ 0.40	$ 0.50
Diluted (in Dollars per share)	$ 0.13	$ 0.17	$ 0.14	$ 0.13	$ 0.21	$ 0.00	$ 0.06	$ 0.13	$ 0.57	$ 0.40	$ 0.49