Fair Value Measurements - Fair Value Measurements (Details) - Fair Value, Recurring [Member] - USD ($) $ in Thousands	Feb. 28, 2022	Aug. 31, 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deferred compensation assets	$ 49,594	$ 51,940
Embedded derivative asset	13,287	16,488
Securities Segregated under Other Regulations	124,928	99,837
Other assets	7,096	6,052
Total assets	1,070,923	738,452
Foreign exchange derivatives		8,506
Total liabilities	575,211	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	49,594	51,940
Embedded derivative asset	0	0
Securities Segregated under Other Regulations	124,928	99,837
Other assets	7,096	6,052
Total assets	183,780	160,282
Foreign exchange derivatives		0
Total liabilities	4,592	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	13,287	16,488
Securities Segregated under Other Regulations	0	0
Other assets	0	0
Total assets	887,143	578,170
Foreign exchange derivatives		8,506
Total liabilities	570,619	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	808,779	544,706
Derivative Liability	568,980	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	2,162	2,453
Derivative Liability	4,592	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	806,617	542,253
Derivative Liability	564,388	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	67,239	19,429
Foreign exchange derivatives	6,231
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	67,239	19,429
Foreign exchange derivatives	6,231
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