Note 12 - 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, 2014	May 31, 2014	Feb. 28, 2014	Nov. 30, 2013	Aug. 31, 2013	May 31, 2013	Feb. 28, 2013	Nov. 30, 2012	Aug. 31, 2014	Aug. 31, 2013	Aug. 31, 2012
Weighted Average Shares Outstanding [Abstract]
Income available to common stockholders (in Dollars)									$ 211,543	$ 198,637	$ 188,809
Income available to common stockholders									42,436	43,890	44,784
Income available to common stockholders (in Dollars per share)									$ 4.98	$ 4.53	$ 4.22
Dilutive effect of stock options and restricted stock									534	734	1,026
Income available to common stockholders plus assumed conversions (in Dollars)									$ 211,543	$ 198,637	$ 188,809
Income available to common stockholders plus assumed conversions	42,386	42,615	43,107	43,773	44,043	44,485	44,455	44,984	42,970	44,624	45,810
Income available to common stockholders plus assumed conversions (in Dollars per share)	$ 1.31	$ 1.21	$ 1.22	$ 1.19	$ 1.16	$ 1.20	$ 1.00	$ 1.11	$ 4.92	$ 4.45	$ 4.12