Earnings Per Share - Weighted Average Shares Outstanding (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Feb. 28, 2021	Feb. 29, 2020	Feb. 28, 2021	Feb. 29, 2020
Basic EPS
Income available to common stockholders	$ 96,643	$ 88,686	$ 197,849	$ 182,643
Basic weighted average common shares (in shares)	37,916	37,875	37,961	37,927
Basic earnings per common share (in USD per share)	$ 2.55	$ 2.34	$ 5.21	$ 4.82
Diluted EPS
Income available to common stockholders plus assumed conversions	$ 96,643	$ 88,686	$ 197,849	$ 182,643
Dilutive effect of stock options and restricted stock (in shares)	704	701	697	655
Diluted weighted average common shares (in shares)	38,620	38,576	38,658	38,582
Diluted earnings per common share (in USD per share)	$ 2.50	$ 2.30	$ 5.12	$ 4.73