Commodity and Other Repurchase Agreements and Collateralized Transactions (Notes)	6 Months Ended
Mar. 31, 2017
Commodity and Other Repurchase Agreements [Abstract]
Repurchase Agreements, Resale Agreements, Securities Borrowed, and Securities Loaned Disclosure [Text Block]	Commodity and Other Repurchase Agreements and Collateralized Transactions Commodity Repurchase Arrangements The Company’s outstanding notes receivable in connection with sale/repurchase agreements, whereby customers sell certain commodity inventory and agree to repurchase the commodity inventory at a future date at a fixed rate, as of March 31, 2017 and September 30, 2016 were $0.6 million and $1.5 million, respectively. Resale and Repurchase Agreements, Securities Lending and Borrowing Agreements, and Margin Securities The Company enters into securities purchased under agreements to resell, securities sold under agreements to repurchase, securities borrowed and securities loaned transactions to, among other things, finance financial instruments, acquire securities to cover short positions, acquire securities for settlement, and to accommodate counterparties’ needs. These agreements are recorded at their contractual amounts plus accrued interest. The related interest is recorded in the condensed consolidated income statements as interest income or interest expense, as applicable. In connection with these agreements and transactions, it is the policy of the Company to receive or pledge cash or securities to adequately collateralize such agreements and transactions in accordance with general industry guidelines and practices. The value of the collateral is valued daily and the Company may require counterparties to deposit additional collateral or return collateral pledged, when appropriate. The carrying amounts of these agreements and transactions approximate fair value due to their short-term nature and the level of collateralization. The Company pledges financial instruments owned to collateralize repurchase agreements and securities loaned agreements. At March 31, 2017, financial instruments owned of $324.6 million were pledged as collateral under repurchase agreements and securities loaned agreements. The counterparty has the right to repledge the collateral in connection with these transactions. These financial instruments owned have been pledged as collateral and have been parenthetically disclosed on the condensed consolidated balance sheet. In addition, as of March 31, 2017, the Company pledged financial instruments owned of $1,160.0 million and securities received under reverse repurchase agreements of which $86.8 million is used to cover collateral for tri-party repurchase agreements. For these securities, the counterparty does not have the right to sell or repledge the collateral. At March 31, 2017, the Company has accepted collateral that it is permitted by contract to sell or repledge. This collateral consists primarily of securities received in reverse repurchase agreements, securities borrowed agreements, and margin securities held on behalf of correspondent brokers. The fair value of such collateral at March 31, 2017, was $957.7 million of which $654.5 million was used to cover securities sold short which are recorded in financial instruments sold, not yet purchased on the condensed consolidated balance sheet. In the normal course of business, this collateral is used by the Company to cover financial instruments sold, not yet purchased, to obtain financing in the form of repurchase agreements, and to meet counterparties’ needs under lending arrangements. At March 31, 2017, substantially all of the above collateral had been delivered against financial instruments sold, not yet purchased or repledged by the Company to obtain financing.

Commodity and Other Repurchase Agreements and Collateralized Transactions

Commodity Repurchase Arrangements

The Company’s outstanding notes receivable in connection with sale/repurchase agreements, whereby customers sell certain commodity inventory and agree to repurchase the commodity inventory at a future date at a fixed rate, as of March 31, 2017 and September 30, 2016 were $0.6 million and $1.5 million, respectively.

Resale and Repurchase Agreements, Securities Lending and Borrowing Agreements, and Margin Securities

The Company enters into securities purchased under agreements to resell, securities sold under agreements to repurchase, securities borrowed and securities loaned transactions to, among other things, finance financial instruments, acquire securities to cover short positions, acquire securities for settlement, and to accommodate counterparties’ needs. These agreements are recorded at their contractual amounts plus accrued interest. The related interest is recorded in the condensed consolidated income statements as interest income or interest expense, as applicable. In connection with these agreements and transactions, it is the policy of the Company to receive or pledge cash or securities to adequately collateralize such agreements and transactions in accordance with general industry guidelines and practices. The value of the collateral is valued daily and the Company may require counterparties to deposit additional collateral or return collateral pledged, when appropriate. The carrying amounts of these agreements and transactions approximate fair value due to their short-term nature and the level of collateralization.

The Company pledges financial instruments owned to collateralize repurchase agreements and securities loaned agreements. At March 31, 2017, financial instruments owned of $324.6 million were pledged as collateral under repurchase agreements and securities loaned agreements. The counterparty has the right to repledge the collateral in connection with these transactions. These financial instruments owned have been pledged as collateral and have been parenthetically disclosed on the condensed consolidated balance sheet.

In addition, as of March 31, 2017, the Company pledged financial instruments owned of $1,160.0 million and securities received under reverse repurchase agreements of which $86.8 million is used to cover collateral for tri-party repurchase agreements. For these securities, the counterparty does not have the right to sell or repledge the collateral.

At March 31, 2017, the Company has accepted collateral that it is permitted by contract to sell or repledge. This collateral consists primarily of securities received in reverse repurchase agreements, securities borrowed agreements, and margin securities held on behalf of correspondent brokers. The fair value of such collateral at March 31, 2017, was $957.7 million of which $654.5 million was used to cover securities sold short which are recorded in financial instruments sold, not yet purchased on the condensed consolidated balance sheet. In the normal course of business, this collateral is used by the Company to cover financial instruments sold, not yet purchased, to obtain financing in the form of repurchase agreements, and to meet counterparties’ needs under lending arrangements. At March 31, 2017, substantially all of the above collateral had been delivered against financial instruments sold, not yet purchased or repledged by the Company to obtain financing.