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, 2018	May 31, 2018	Feb. 28, 2018	Nov. 30, 2017	Aug. 31, 2017	May 31, 2017	Feb. 28, 2017	Nov. 30, 2016	Aug. 31, 2018		Aug. 31, 2017		Aug. 31, 2016
Revenues(1)
Revenues from clients		$ 345,861	$ 339,911	$ 335,231	$ 329,141	$ 326,642	$ 312,120	$ 294,354	$ 288,063	$ 1,350,145	[1]	$ 1,221,179	[1]	$ 1,127,092	[1]
UNITED STATES
Revenues(1)
Revenues from clients	[1]									841,908		784,146		755,492
UNITED KINGDOM
Revenues(1)
Revenues from clients	[1]									332,006		163,732		154,902
All Other European Countries [Member]
Revenues(1)
Revenues from clients	[1]									55,583		166,600		122,780
Asia Pacific [Member]
Revenues(1)
Revenues from clients	[1]									$ 120,648		$ 106,701		$ 93,918

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