Income Taxes - Reconciliation of the Statutory Tax Rates to the Effective Tax Rates (Details)	12 Months Ended
	Aug. 31, 2018	Aug. 31, 2017	Aug. 31, 2016
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Statutory federal income tax rate	25.70%	35.00%	35.00%
State and local income taxes, net of federal income tax benefit	0.70%	12.10%	0.30%
Patronage earnings	(13.60%)	91.70%	(21.20%)
Domestic production activities deduction	(8.40%)	30.50%	(12.10%)
Export activities at rates other than the U.S. statutory rate	6.10%	51.60%	(3.00%)
U.S. tax reform	(23.20%)	0.00%	0.00%
Intercompany transfer of business assets	(6.10%)	0.00%	0.00%
Increase in unrecognized tax benefits	6.80%	0.00%	0.00%
Valuation allowance	(3.40%)	(77.10%)	25.40%
Tax credits	0.70%	22.80%	(14.10%)
Crack spread contingency	0.00%	4.80%	(5.30%)
Other	(0.80%)	(7.00%)	(0.30%)
Effective tax rate	(15.50%)	164.40%	4.70%