Fair Value Measurements - Recurring Fair Value Measurements (Details) - USD ($) $ in Thousands	Aug. 31, 2021	Aug. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Embedded Derivative, Fair Value of Embedded Derivative Asset	$ 16,500
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deferred Compensation Assets, at Fair Value	51,940	$ 47,669
Embedded Derivative, Fair Value of Embedded Derivative Asset	16,488	18,998
Securities Segregated under Other Regulations	99,837	85,950
Other assets	6,052	5,276
Total assets	738,452	530,961
Total liabilities	454,368	421,630
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deferred Compensation Assets, at Fair Value	0	0
Embedded Derivative, Fair Value of Embedded Derivative Asset	0	0
Securities Segregated under Other Regulations	0
Other assets	0	0
Total assets	0	0
Total liabilities	0	0
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deferred Compensation Assets, at Fair Value	0	0
Embedded Derivative, Fair Value of Embedded Derivative Asset	16,488	18,998
Securities Segregated under Other Regulations	0
Other assets	0	0
Total assets	578,170	386,304
Total liabilities	452,753	415,593
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deferred Compensation Assets, at Fair Value	51,940	47,669
Embedded Derivative, Fair Value of Embedded Derivative Asset	0	0
Securities Segregated under Other Regulations	99,837	85,950
Other assets	6,052	5,276
Total assets	160,282	144,657
Total liabilities	1,615	6,037
Fair Value, Measurements, Recurring | Commodity derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset	544,706	361,545
Derivative Liability	445,862	352,163
Fair Value, Measurements, Recurring | Commodity derivatives | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset	0	0
Derivative Liability	0	0
Fair Value, Measurements, Recurring | Commodity derivatives | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset	542,253	355,783
Derivative Liability	444,247	346,126
Fair Value, Measurements, Recurring | Commodity derivatives | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset	2,453	5,762
Derivative Liability	1,615	6,037
Fair Value, Measurements, Recurring | Foreign currency derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign Currency Contract, Asset, Fair Value Disclosure	19,429	11,523
Foreign Currency Contracts, Liability, Fair Value Disclosure	8,506	69,467
Fair Value, Measurements, Recurring | Foreign currency derivatives | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign Currency Contract, Asset, Fair Value Disclosure	0	0
Foreign Currency Contracts, Liability, Fair Value Disclosure	0	0
Fair Value, Measurements, Recurring | Foreign currency derivatives | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign Currency Contract, Asset, Fair Value Disclosure	19,429	11,523
Foreign Currency Contracts, Liability, Fair Value Disclosure	8,506	69,467
Fair Value, Measurements, Recurring | Foreign currency derivatives | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign Currency Contract, Asset, Fair Value Disclosure	0	0
Foreign Currency Contracts, Liability, Fair Value Disclosure	$ 0	$ 0