Consolidated Statements of Income - Unaudited - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	May 31, 2020	May 31, 2019	May 31, 2020	May 31, 2019
Income Statement [Abstract]
Revenue	$ 374,083	$ 364,533	$ 1,110,521	$ 1,071,068
Operating expenses
Cost of services	170,703	163,832	511,878	495,716
Selling, general and administrative	81,740	83,461	257,560	248,885
Total operating expenses	252,443	247,293	769,438	744,601
Operating income	121,640	117,240	341,083	326,467
Other expenses
Interest expense, net	(2,211)	(4,377)	(8,003)	(13,046)
Other (expense) income, net	(289)	521	(2,090)	255
Income before income taxes	119,140	113,384	330,990	313,676
Provision for income taxes	17,924	21,119	47,131	52,413
Net income	$ 101,216	$ 92,265	$ 283,859	$ 261,263
Basic earnings per common share (in USD per share)	$ 2.67	$ 2.41	$ 7.49	$ 6.85
Diluted earnings per common share (in USD per share)	$ 2.63	$ 2.37	$ 7.36	$ 6.73
Basic weighted average common shares (in shares)	37,885	38,223	37,912	38,128
Diluted weighted average common shares (in shares)	38,481	38,993	38,548	38,807