Commodity and Other Repurchase Agreements and Collateralized Transactions (Notes)	3 Months Ended
Dec. 31, 2016
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 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 December 31, 2016 and September 30, 2016 were $5.8 million and $1.5 million, respectively. The Company enters into securities purchased under agreements to resell and payables under repurchase agreements primarily to finance financial instruments, acquire securities to cover short positions or to acquire securities for settlement. 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. At December 31, 2016, on a settlement date basis, financial instruments owned of $482.4 million were pledged as collateral under repurchase 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 December 31, 2016, the Company pledged settlement date financial instruments owned of $912.7 million and securities received under reverse repurchase agreements of $206.5 million 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 December 31, 2016, the Company has accepted collateral that it is permitted by contract or custom to sell or repledge. This collateral consists primarily of securities received in reverse repurchase agreements. The fair value of such collateral at December 31, 2016, was approximately $766.3 million of which $558.3 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 and to obtain financing in the form of repurchase agreements. At December 31, 2016, substantially all of the above collateral had been delivered against financial instruments sold, not yet purchased or repledged by the Company to obtain financing. The Company has margin securities, securities borrowed and securities held on behalf of correspondent brokers, on terms which permit it to repledge the securities to others. At December 31, 2016, the Company had obtained and had available securities, on a settlement date basis, with a fair value of $202.7 million on such terms, of which $30.3 million have either been pledged or otherwise transferred to others in connection with the Company’s financing activities or to satisfy commitments under short sales.

Commodity and Other Repurchase Agreements and Collateralized Transactions

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 December 31, 2016 and September 30, 2016 were $5.8 million and $1.5 million, respectively.

The Company enters into securities purchased under agreements to resell and payables under repurchase agreements primarily to finance financial instruments, acquire securities to cover short positions or to acquire securities for settlement. 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. At December 31, 2016, on a settlement date basis, financial instruments owned of $482.4 million were pledged as collateral under repurchase 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 December 31, 2016, the Company pledged settlement date financial instruments owned of $912.7 million and securities received under reverse repurchase agreements of $206.5 million 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 December 31, 2016, the Company has accepted collateral that it is permitted by contract or custom to sell or repledge. This collateral consists primarily of securities received in reverse repurchase agreements. The fair value of such collateral at December 31, 2016, was approximately $766.3 million of which $558.3 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 and to obtain financing in the form of repurchase agreements. At December 31, 2016, substantially all of the above collateral had been delivered against financial instruments sold, not yet purchased or repledged by the Company to obtain financing.

The Company has margin securities, securities borrowed and securities held on behalf of correspondent brokers, on terms which permit it to repledge the securities to others. At December 31, 2016, the Company had obtained and had available securities, on a settlement date basis, with a fair value of $202.7 million on such terms, of which $30.3 million have either been pledged or otherwise transferred to others in connection with the Company’s financing activities or to satisfy commitments under short sales.