Segment Information - Results of Operations (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Aug. 31, 2020	May 31, 2020	Feb. 28, 2020	Nov. 30, 2019	Aug. 31, 2019	May 31, 2019	Feb. 28, 2019	Nov. 30, 2018	Aug. 31, 2020	Aug. 31, 2019	Aug. 31, 2018
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue from clients	$ 383,590	$ 374,083	$ 369,780	$ 366,658	$ 364,283	$ 364,533	$ 354,895	$ 351,640	$ 1,494,111	$ 1,435,351	$ 1,350,145
Segment operating profit	$ 98,577	$ 121,640	$ 106,257	$ 113,186	$ 111,568	$ 117,240	$ 108,688	$ 100,539	439,660	438,035	366,204
Depreciation and amortization									57,614	60,463	57,285
Stock-based compensation									36,579	32,400	31,516
Capital expenditures									77,642	59,370	33,520
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue from clients									885,082	854,675	806,426
EMEA
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue from clients									422,203	408,084	387,589
Segment operating profit									179,831	179,258	148,977
Depreciation and amortization									14,338	14,703	15,710
Stock-based compensation									6,576	5,320	4,857
Capital expenditures									2,079	2,595	3,140
Asia Pacific
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue from clients									142,464	132,713	120,648
Segment operating profit									90,920	79,403	69,132
Depreciation and amortization									7,148	5,742	4,122
Stock-based compensation									1,223	928	645
Capital expenditures									15,359	13,128	10,022
Americas
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue from clients									929,444	894,554	841,908
Segment operating profit									168,909	179,374	148,095
Depreciation and amortization									36,128	40,018	37,453
Stock-based compensation									28,780	26,152	26,014
Capital expenditures									$ 60,204	$ 43,647	$ 20,358