Income taxes - reconciliation to effective tax rate (Details)	12 Months Ended
	Aug. 31, 2024	Aug. 31, 2023	Aug. 31, 2022
Income Tax Disclosure [Abstract]
Federal statutory rate	21.00%	21.00%	21.00%
State income taxes, net of federal benefit	1.80%	(5.80%)	0.40%
Foreign income taxed at non-U.S. rates	0.30%	3.00%	(3.00%)
Non-taxable income	(0.30%)	(2.50%)	(2.70%)
Non-deductible expenses	0.90%	4.90%	3.00%
Change in valuation allowance	13.20%	(6.00%)	(9.00%)
Tax benefits from restructuring	0.00%	(1.10%)	0.00%
Uncertain tax positions	0.40%	0.50%	1.30%
Non-controlling interest	10.10%	2.90%	1.20%
Goodwill impairment	7.20%	0.00%	0.00%
Tax credits	(0.50%)	(2.80%)	(1.00%)
Conversion of equity investment	0.00%	0.00%	(11.80%)
Change in tax basis in foreign assets	(2.20%)	0.00%	0.00%
Change in outside basis difference	(1.40%)	(1.90%)	0.00%
Change in measurement of prior year tax positions	0.00%	(3.50%)	0.00%
Other	0.30%	(1.00%)	(0.20%)
Effective income tax rate	8.80%	(34.30%)	(0.80%)