Note 7 - Segment Information - Revenues from Countries That Are 10% Or More of Revenues (Details) - USD ($) $ 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(1)
Revenues from clients		$ 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]
UNITED STATES
Revenues(1)
Revenues from clients	[1]									784,146		755,492		678,774
UNITED KINGDOM
Revenues(1)
Revenues from clients	[1]									163,732		154,902		144,769
All Other European Countries [Member]
Revenues(1)
Revenues from clients	[1]									166,600		122,780		106,753
Asia Pacific [Member]
Revenues(1)
Revenues from clients	[1]									$ 106,701		$ 93,918		$ 76,472

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