Note 7 - Segment Information - Results of Operations (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 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]
Segment operating profit		88,356	$ 93,265	$ 95,485	$ 89,098	82,428	$ 87,642	$ 91,746	$ 90,319	366,204		352,135		349,676
Total assets		1,419,448				1,413,315				1,419,448		1,413,315		1,019,161
Depreciation and amortization										57,285		48,294		38,052
Stock-based compensation										31,516		34,183		29,793
Capital expenditures										33,520		36,862		47,740
UNITED STATES
Revenues from clients	[1]									841,908		784,146		755,492
Segment operating profit										148,095		137,104		165,251
Total assets		724,259				703,941				724,259		703,941		654,796
Depreciation and amortization										37,453		35,244		31,529
Stock-based compensation										26,014		30,247		25,776
Capital expenditures										20,358		29,561		38,631
Europe [Member]
Revenues from clients										387,589		330,332		277,682
Segment operating profit										148,977		153,676		131,410
Total assets		585,497				609,368				585,497		609,368		279,864
Depreciation and amortization										15,710		9,837		4,220
Stock-based compensation										4,857		3,320		3,459
Capital expenditures										3,140		2,385		4,092
Asia Pacific [Member]
Revenues from clients	[1]									120,648		106,701		93,918
Segment operating profit										69,132		61,355		53,015
Total assets		$ 109,692				$ 100,006				109,692		100,006		84,501
Depreciation and amortization										4,122		3,213		2,303
Stock-based compensation										645		616		558
Capital expenditures										$ 10,022		$ 4,916		$ 5,017

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