Receivables From Customers, Net and Notes Receivable, Net (Notes)	6 Months Ended
Mar. 31, 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 $10.7 million and $10.2 million as of March 31, 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 March 31, 2019 and September 30, 2018, respectively. During the three months ended March 31, 2019, the Company recorded bad debt expense of $0.7 million. The bad debt expense was primarily related to client account deficits in the Company’s Commercial Hedging segment. During the three months ended March 31, 2018, the Company recorded bad debt expense of $0.2 million. The bad debt expense was primarily related to a precious metals client trading account deficit in the Company’s Physical Commodities segment, partially offset by bad debt recoveries in the Physical Commodities and Commercial Hedging segments. During the six months ended March 31, 2019, the Company recorded bad debt expense of $1.0 million. The bad debt expense was primarily related to client account deficits in the Company’s Commercial Hedging and Clearing and Execution services segments. Additionally, during the six months ended March 31, 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 six months ended March 31, 2019. During the six months ended March 31, 2018, the Company recorded bad debt expense of $0.3 million. Additionally, within the Company’s Physical Commodities segment, it 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 $10.7 million and $10.2 million as of March 31, 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 March 31, 2019 and September 30, 2018, respectively.

During the three months ended March 31, 2019, the Company recorded bad debt expense of $0.7 million. The bad debt expense was primarily related to client account deficits in the Company’s Commercial Hedging segment. During the three months ended March 31, 2018, the Company recorded bad debt expense of $0.2 million. The bad debt expense was primarily related to a precious metals client trading account deficit in the Company’s Physical Commodities segment, partially offset by bad debt recoveries in the Physical Commodities and Commercial Hedging segments.

During the six months ended March 31, 2019, the Company recorded bad debt expense of $1.0 million. The bad debt expense was primarily related to client account deficits in the Company’s Commercial Hedging and Clearing and Execution services segments. Additionally, during the six months ended March 31, 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 six months ended March 31, 2019.

During the six months ended March 31, 2018, the Company recorded bad debt expense of $0.3 million. Additionally, within the Company’s Physical Commodities segment, it 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.