Consolidated Statements of Income - Unaudited - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Feb. 28, 2021	Feb. 29, 2020	Feb. 28, 2021	Feb. 29, 2020
Income Statement [Abstract]
Revenues	$ 391,788	$ 369,780	$ 779,993	$ 736,438
Operating expenses
Cost of services	195,523	176,218	383,611	341,175
Selling, general and administrative	80,132	87,305	159,219	175,820
Total operating expenses	275,655	263,523	542,830	516,995
Operating income	116,133	106,257	237,163	219,443
Other income (expense)
Interest expense, net	(1,814)	(2,661)	(2,843)	(5,792)
Other income (expense), net	347	(487)	578	(1,801)
Income before income taxes	114,666	103,109	234,898	211,850
Provision for income taxes	18,023	14,423	37,049	29,207
Net income	$ 96,643	$ 88,686	$ 197,849	$ 182,643
Basic earnings per common share (in USD per share)	$ 2.55	$ 2.34	$ 5.21	$ 4.82
Diluted earnings per common share (in USD per share)	$ 2.50	$ 2.30	$ 5.12	$ 4.73
Basic weighted average common shares (in shares)	37,916	37,875	37,961	37,927
Diluted weighted average common shares (in shares)	38,620	38,576	38,658	38,582