Note 21 - Unaudited Quarterly Financial Data - Unaudited Quarterly Results (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended																12 Months Ended
	Aug. 31, 2017		May 31, 2017		Feb. 28, 2017		Nov. 30, 2016		Aug. 31, 2016		May 31, 2016		Feb. 28, 2016		Nov. 30, 2015		Aug. 31, 2017		Aug. 31, 2016		Aug. 31, 2015
Revenues	$ 326,642		$ 312,120		$ 294,354		$ 288,063		$ 287,291		$ 287,501		$ 281,796		$ 270,504		$ 1,221,179	[1]	$ 1,127,092	[1]	$ 1,006,768	[1]
Cost of services	161,269		146,426		131,635		127,250		124,160		124,602		123,911		114,736		566,580		487,409		405,339
Selling, general and administrative	82,945		78,052		70,973		70,494		75,397		73,609		72,541		68,460		302,464		290,007		269,511
Operating income	82,428		87,642		91,746		90,319		87,734		89,290		85,344		87,308		352,135		349,676		331,918
Net income	$ 59,552		$ 65,414		$ 66,710		$ 66,583		$ 144,306		$ 66,781		$ 67,763		$ 59,965		$ 258,259		$ 338,815		$ 241,051
Diluted earnings per common share(1) (in dollars per share)	$ 1.52	[2]	$ 1.66	[2]	$ 1.68	[2]	$ 1.66	[2]	$ 3.55	[2]	$ 1.62	[2]	$ 1.63	[2]	$ 1.43	[2]	$ 6.51		$ 8.19		$ 5.71
Weighted average common shares (diluted) (in shares)	39,281		39,457		39,700		40,100		40,673		41,189		41,536		42,063		39,642		41,365		42,235

[1] Revenues are attributed to countries based on the location of the client.

[2] Diluted earnings per common share is calculated independently for each of the periods presented. Accordingly, the sum of the quarterly EPS amounts may not equal the total for the fiscal year.