Quarterly Financial Information, Unaudited (Details) (USD $)	3 Months Ended								12 Months Ended
	Feb. 28, 2013	Nov. 30, 2012	Aug. 31, 2012	May 31, 2012	Feb. 29, 2012	Nov. 30, 2011	Aug. 31, 2011	May 31, 2011	Feb. 28, 2013	Feb. 29, 2012	Feb. 28, 2011
Quarterly Financial Information Disclosure [Abstract]
Net sales	$ 140,391,000	$ 149,675,000	$ 153,385,000	$ 127,143,000	$ 123,625,000	$ 116,493,000	$ 114,661,000	$ 114,333,000	$ 570,594,238	$ 469,112,410	$ 380,649,407
Gross profit	37,992,000	45,003,000	43,312,000	37,866,000	32,331,000	30,807,000	30,380,000	31,069,000
Net income	$ 13,233,000	$ 15,364,000	$ 15,873,000	$ 15,986,000	$ 11,644,000	$ 10,021,000	$ 9,606,000	$ 9,465,000	$ 60,456,206	$ 40,735,796	$ 34,962,641
Basic earnings per common share (usd per share)	$ 0.52	$ 0.61	$ 0.63	$ 0.63	$ 0.47	$ 0.40	$ 0.38	$ 0.38	$ 2.39	$ 1.62	$ 1.40
Diluted earnings per common share (usd per share)	$ 0.52	$ 0.60	$ 0.62	$ 0.63	$ 0.46	$ 0.40	$ 0.38	$ 0.38	$ 2.37	$ 1.61	$ 1.39