Receivables From Customers, Net and Notes Receivable, Net (Notes)	9 Months Ended
Jun. 30, 2019
Receivables from customers and notes receivable, net [Abstract]
Financing Receivables [Text Block]	Allowance for Doubtful Accounts The allowance for doubtful accounts related to receivables from clients was $11.2 million and $10.2 million as of June 30, 2019 and September 30, 2018, respectively. The allowance for doubtful accounts related to deposits with and receivables from broker-dealers, clearing organizations, and counterparties was $45.6 million and $48.0 million as of June 30, 2019 and September 30, 2018, respectively. During the three months ended June 30, 2019, the Company recorded bad debt expense of $0.5 million. The bad debt expense was primarily related to agricultural and metals OTC client trading account deficits in the Company’s Commercial Hedging segment. During the three months ended June 30, 2018, the Company recorded bad debt expense of $1.6 million. The bad debt expense was primarily related to agricultural OTC client trading account deficits in the Company’s Commercial Hedging segment partially offset by the recovery of a precious metals client trading account deficit in the Company’s Physical Commodities segment. During the nine months ended June 30, 2019, the Company recorded bad debt expense of $1.5 million. The bad debt expense was primarily related to agricultural and metals OTC client trading account deficits in the Company’s Commercial Hedging. Additionally, during the nine months ended June 30, 2019, the Company reached settlements with clients, paying $8.4 million related to demurrage, dead freight, and other penalty charges regarding coal supplied during fiscal 2017. The settlement amount paid was less than the accrued liability for the transactions recorded during fiscal 2017 and fiscal 2018, and accordingly the Company recorded a recovery on the bad debt on physical coal of $2.4 million in the nine months ended June 30, 2019. During the nine months ended June 30, 2018, the Company recorded bad debt expense of $1.9 million primarily related to agricultural OTC client trading account deficits in the Company’s Commercial Hedging segment. Additionally, within the Company’s Physical Commodities segment, the Company recorded an additional provision of $1.0 million related to the bad debt on physical coal for amounts due to the Company from a coal supplier for demurrage and other charges related to contracts with delivery dates subsequent to September 30, 2017.

Allowance for Doubtful Accounts

The allowance for doubtful accounts related to receivables from clients was $11.2 million and $10.2 million as of June 30, 2019 and September 30, 2018, respectively. The allowance for doubtful accounts related to deposits with and receivables from broker-dealers, clearing organizations, and counterparties was $45.6 million and $48.0 million as of June 30, 2019 and September 30, 2018, respectively.

During the three months ended June 30, 2019, the Company recorded bad debt expense of $0.5 million. The bad debt expense was primarily related to agricultural and metals OTC client trading account deficits in the Company’s Commercial Hedging segment. During the three months ended June 30, 2018, the Company recorded bad debt expense of $1.6 million. The bad debt expense was primarily related to agricultural OTC client trading account deficits in the Company’s Commercial Hedging segment partially offset by the recovery of a precious metals client trading account deficit in the Company’s Physical Commodities segment.

During the nine months ended June 30, 2019, the Company recorded bad debt expense of $1.5 million. The bad debt expense was primarily related to agricultural and metals OTC client trading account deficits in the Company’s Commercial Hedging. Additionally, during the nine months ended June 30, 2019, the Company reached settlements with clients, paying $8.4 million related to demurrage, dead freight, and other penalty charges regarding coal supplied during fiscal 2017. The settlement amount paid was less than the accrued liability for the transactions recorded during fiscal 2017 and fiscal 2018, and accordingly the Company recorded a recovery on the bad debt on physical coal of $2.4 million in the nine months ended June 30, 2019.

During the nine months ended June 30, 2018, the Company recorded bad debt expense of $1.9 million primarily related to agricultural OTC client trading account deficits in the Company’s Commercial Hedging segment. Additionally, within the Company’s Physical Commodities segment, the Company recorded an additional provision of $1.0 million related to the bad debt on physical coal for amounts due to the Company from a coal supplier for demurrage and other charges related to contracts with delivery dates subsequent to September 30, 2017.