Fair Value Measurements - Fair Value Measurements (Details) - Fair Value, Recurring [Member] - USD ($) $ in Thousands	Nov. 30, 2021	Aug. 31, 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deferred compensation assets	$ 51,113	$ 51,940
Embedded derivative asset	13,034	16,488
Securities Segregated under Other Regulations	96,447	99,837
Other assets	6,616	6,052
Total assets	628,062	738,452
Foreign exchange derivatives		8,506
Total liabilities	324,928	454,368
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deferred compensation assets	51,113	51,940
Embedded derivative asset	0	0
Securities Segregated under Other Regulations	96,447	99,837
Other assets	6,616	6,052
Total assets	157,017	160,282
Foreign exchange derivatives		0
Total liabilities	3,860	1,615
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deferred compensation assets	0	0
Embedded derivative asset	13,034	16,488
Securities Segregated under Other Regulations	0	0
Other assets	0	0
Total assets	471,045	578,170
Foreign exchange derivatives		8,506
Total liabilities	321,068	452,753
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deferred compensation assets	0	0
Embedded derivative asset	0	0
Securities Segregated under Other Regulations	0	0
Other assets	0	0
Total assets	0	0
Foreign exchange derivatives		0
Total liabilities	0	0
Commodity derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset	452,369	544,706
Derivative Liability	297,465	445,862
Commodity derivatives | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset	2,841	2,453
Derivative Liability	3,860	1,615
Commodity derivatives | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset	449,528	542,253
Derivative Liability	293,605	444,247
Commodity derivatives | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset	0	0
Derivative Liability	0	0
Foreign exchange derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign exchange derivatives	8,483	19,429
Foreign exchange derivatives	27,463
Foreign exchange derivatives | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign exchange derivatives	0	0
Foreign exchange derivatives	0
Foreign exchange derivatives | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign exchange derivatives	8,483	19,429
Foreign exchange derivatives	27,463
Foreign exchange derivatives | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign exchange derivatives	0	$ 0
Foreign exchange derivatives	$ 0