Note 11 - Common Stock and Earnings Per Share (Details) - Weighted Average Shares Outstanding (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Aug. 31, 2013	May 31, 2013	Feb. 28, 2013	Nov. 30, 2012	Aug. 31, 2012	May 31, 2012	Feb. 29, 2012	Nov. 30, 2011	Aug. 31, 2013	Aug. 31, 2012	Aug. 31, 2011
Weighted Average Shares Outstanding [Abstract]
Income available to common stockholders (in Dollars)									$ 198,637	$ 188,809	$ 171,046
Income available to common stockholders									43,890	44,784	45,953
Income available to common stockholders (in Dollars per share)									$ 4.53	$ 4.22	$ 3.72
Dilutive effect of stock options and restricted stock									734	1,026	1,402
Income available to common stockholders plus assumed conversions (in Dollars)									$ 198,637	$ 188,809	$ 171,046
Income available to common stockholders plus assumed conversions	44,043	44,485	44,455	44,984	45,152	45,736	45,707	46,103	44,624	45,810	47,355
Income available to common stockholders plus assumed conversions (in Dollars per share)	$ 1.16	$ 1.20	$ 1.00	$ 1.11	$ 1.08	$ 1.05	$ 1.02	$ 0.99	$ 4.45	$ 4.12	$ 3.61