Selected Quarterly Financial Data (Unaudited) (Details) (USD $)	3 Months Ended								12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2011
Selected Quarterly Financial Data (Unaudited)
Net sales	$ 6,897,000	$ 7,242,000	$ 6,936,000	$ 6,506,000	$ 5,986,000	$ 6,706,000	$ 5,989,000	$ 5,950,000	$ 27,581,000	$ 24,631,000	$ 16,827,000
Gross profit	2,707,000	2,865,000	2,812,000	2,574,000	2,053,000	2,827,000	2,790,000	2,104,000	10,958,000	9,774,000	6,341,000
Net income	2,633,000	607,000	476,000	493,000	1,158,000	1,113,000	875,000	486,000	4,209,000	3,632,000	1,730,000
Net income per share-
Basic (in dollars per share)	$ 0.48	$ 0.11	$ 0.09	$ 0.09	$ 0.21	$ 0.21	$ 0.16	$ 0.09	$ 0.77	$ 0.67	$ 0.32
Diluted (in dollars per share)	$ 0.47	$ 0.11	$ 0.08	$ 0.08	$ 0.20	$ 0.20	$ 0.16	$ 0.09	$ 0.74	$ 0.66	$ 0.32
Additional disclosure
Abnormal production costs	282,000	161,000	481,000	233,000	575,000	236,000	218,000	198,000	1,157,000	1,174,000	439,000
Income tax benefit due to reduction in valuation allowance of deferred tax assets	$ 1,912,000				$ 892,000				$ 1,912,000	$ 892,000	$ 552,000