Summary of Unaudited Quarterly Results of Operations (Detail) (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
Schedule Of Quarterly Financial Information [Line Items]
Net sales	$ 31,960,024	$ 31,719,922	$ 33,334,070	$ 39,434,770	$ 43,559,995		$ 36,987,260		$ 42,039,282		$ 38,935,456		$ 136,448,786	$ 161,521,993
Gross profit	3,092,650	2,884,278	3,776,798	4,647,758	4,630,364		3,932,881		4,886,403		4,156,825
Net earnings	$ 1,249,571	$ 1,150,058	$ 1,644,329	$ 2,091,854	$ 2,204,896		$ 1,799,249		$ 2,314,908		$ 1,831,411		$ 6,135,812	$ 8,150,464
Basic	$ 0.18	$ 0.17	$ 0.24	$ 0.31	$ 0.32	[1]	$ 0.26	[1]	$ 0.34	[1]	$ 0.27	[1]	$ 0.90	$ 1.20
Diluted	$ 0.18	$ 0.17	$ 0.24	$ 0.31	$ 0.32	[1]	$ 0.26	[1]	$ 0.34	[1]	$ 0.27	[1]	$ 0.90	$ 1.20

[1] The sum of the quarterly earnings per share does not equal the annual amount reported because per share amounts were computed independently for each quarter.