Note 12 - Common Stock and Earnings Per Share - Weighted Average Shares Outstanding (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Nov. 30, 2016	Nov. 30, 2015
Income available to common stockholders, net income (numerator)	$ 66,583	$ 59,965
Basic weighted average common shares (in shares)	39,827	41,387
Basic earnings per common share (in dollars per share)	$ 1.67	$ 1.45
Dilutive effect of stock options and restricted stock, weighted average common share (denominator) (in shares)	271	676
Income available to common stockholders plus assumed conversions, net income (numerator)	$ 66,583	$ 59,965
Diluted weighted average common shares (in shares)	40,100	42,063
Diluted earnings per common share (in dollars per share)	$ 1.66	$ 1.43