Derivative Financial Instruments and Hedging Activities - Gross Fair Values of Derivative Assets, Derivative Liabilities, and Margin Deposits (Cash Collateral) (Details) - USD ($) $ in Thousands	Aug. 31, 2021	Aug. 31, 2020
Reconciliation of gross and net fair value of assets and liabilities subject to offsetting arrangements [Line Items]
Gross Amounts Recognized	$ 568,749	$ 358,300
Derivative asset, fair value, gross amount not offset on Balance sheet	9,756	12,365
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	558,993	345,935
Derivative Liability, Fair Value, Gross Liability	453,367	412,809
Derivative Liability, Collateral, Right to Reclaim Cash, Offset	2,485	956
Derivative liability, fair value, gross amount not offset on balance sheet	9,756	14,963
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	441,126	396,890
Not Designated as Hedging Instrument | Commodity derivatives
Reconciliation of gross and net fair value of assets and liabilities subject to offsetting arrangements [Line Items]
Gross Amounts Recognized	532,832	327,493
Derivative asset, fair value, gross amount not offset on Balance sheet	4,174	2,980
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	528,658	324,513
Derivative Liability, Fair Value, Gross Liability	444,861	343,343
Derivative Liability, Collateral, Right to Reclaim Cash, Offset	2,485	956
Derivative liability, fair value, gross amount not offset on balance sheet	4,174	5,578
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	438,202	336,809
Not Designated as Hedging Instrument | Foreign exchange derivatives
Reconciliation of gross and net fair value of assets and liabilities subject to offsetting arrangements [Line Items]
Gross Amounts Recognized	19,429	11,809
Derivative asset, fair value, gross amount not offset on Balance sheet	5,582	9,385
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	13,847	2,424
Derivative Liability, Fair Value, Gross Liability	8,506	69,466
Derivative Liability, Collateral, Right to Reclaim Cash, Offset	0	0
Derivative liability, fair value, gross amount not offset on balance sheet	5,582	9,385
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	2,924	60,081
Not Designated as Hedging Instrument | Embedded derivative asset
Reconciliation of gross and net fair value of assets and liabilities subject to offsetting arrangements [Line Items]
Gross Amounts Recognized	16,488	18,998
Derivative asset, fair value, gross amount not offset on Balance sheet	0	0
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	$ 16,488	$ 18,998