Consolidated Statements of Income - Unaudited - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Feb. 29, 2020	Feb. 28, 2019	Feb. 29, 2020	Feb. 28, 2019
Income Statement [Abstract]
Revenue	$ 369,780	$ 354,895	$ 736,438	$ 706,535
Operating expenses
Cost of services	176,218	165,108	341,175	331,884
Selling, general and administrative	87,305	81,099	175,820	165,424
Total operating expenses	263,523	246,207	516,995	497,308
Operating income	106,257	108,688	219,443	209,227
Other expenses
Interest expense, net	(2,661)	(4,211)	(5,792)	(8,670)
Other expense, net	(487)	(128)	(1,801)	(265)
Income before income taxes	103,109	104,349	211,850	200,292
Provision for income taxes	14,423	19,647	29,207	31,294
Net income	$ 88,686	$ 84,702	$ 182,643	$ 168,998
Basic earnings per common share (in USD per share)	$ 2.34	$ 2.23	$ 4.82	$ 4.44
Diluted earnings per common share (in USD per share)	$ 2.30	$ 2.19	$ 4.73	$ 4.37
Basic weighted average common shares (in shares)	37,875	38,055	37,927	38,081
Diluted weighted average common shares (in shares)	38,576	38,619	38,582	38,714