Earnings Per Share (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
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Stockholders' Equity Note, Stock Split, Conversion Ratio									2
Numerator:
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
Denominator:
Denominator for basic earnings per common share-weighted average shares (shares)									25,320,147	25,131,754	24,922,700
Effect of dilutive securities:
Employee and Director stock awards (shares)									240,447	230,366	278,608
Denominator for diluted earnings per common share (shares)									25,560,594	25,362,120	25,201,308
Earnings per share basic and diluted:
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