StoneX (SNEX) 10-K 12 Dec 18 2018 FY Annual report Financial data

DEI Document

DEI Document - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Dec. 10, 2018	Mar. 31, 2018
Document and Entity Information [Abstract]
Entity Registrant Name	INTL FCSTONE INC.
Trading Symbol	INTL
Entity Central Index Key	913,760
Current Fiscal Year End Date	--09-30
Entity Filer Category	Accelerated Filer
Document Type	10-K
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Common Stock, Shares Outstanding		18,915,667
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 565.4

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017
ASSETS
Cash and cash equivalents	$ 342.3	$ 314.9
Cash, securities and other assets segregated under federal and other regulations (including $643.3 and $54.5 at fair value at September 30, 2018 and September 30, 2017, respectively)	1,408.7	518.8
Securities purchased under agreements to resell	870.8	406.6
Securities Borrowed	225.5	86.6
Deposits with and receivables from broker-dealers, clearing organizations and counterparties (including $517.4 and $204.7 at fair value at September 30, 2018 and September 30, 2017, respectively)	2,234.5	2,625.1
Receivables from customers, net	288	232.7
Notes receivable, net	3.8	10.6
Income taxes receivable	0.3	0.4
Financial instruments owned, at fair value (includes securities pledged as collateral that can be sold or repledged of $123.0 and $19.4 at September 30, 2018 and September 30, 2017, respectively)	2,054.8	1,731.8
Physical commodities inventory (including $156.9 and $73.2 at fair value at September 30, 2018 and September 30, 2017, respectively)	222.5	124.8
Deferred income taxes, net	19.8	42.6
Property and equipment, net	42.4	38.7
Goodwill and intangible assets, net	59.8	59.4
Other assets	51.5	50.4
Total assets	7,824.7	6,243.4
Liabilities:
Accounts payable and other accrued liabilities (including $0.0 and $1.0 at fair value at September 30, 2018 and September 30, 2017)	145.4	135.6
Payable to:
Customers	3,639.6	3,072.9
Broker-dealers, clearing organizations and counterparties (including $0.0 and $4.8 at fair value at September 30, 2018 and September 30, 2017, respectively)	89.5	125.7
Lenders under loans	355.2	230.2
Income taxes payable	8.6	7.3
Securities sold under agreements to repurchase	1,936.7	1,393.1
Securities Loaned	277.9	111.1
Financial instruments sold, not yet purchased, at fair value	866.5	717.6
Total liabilities	7,319.4	5,793.5
Commitments and contingencies (Note 11)
Stockholders’ equity:
Preferred stock, $0.01 par value. Authorized 1,000,000 shares; no shares issued or outstanding	0	0
Common stock, $0.01 par value. Authorized 30,000,000 shares; 21,030,497 issued and 18,908,540 outstanding at September 30, 2018 and 20,855,243 issued and 18,733,286 outstanding at September 30, 2017	0.2	0.2
Common stock in treasury, at cost - 2,121,957 shares at September 30, 2018 and 2017	(46.3)	(46.3)
Additional paid-in capital	267.5	259
Retained earnings	317	261.5
Accumulated other comprehensive loss, net	(33.1)	(24.5)
Total stockholders' equity	505.3	449.9
Total liabilities and stockholders' equity	$ 7,824.7	$ 6,243.4

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017
ASSETS
Securities and other assets segregated, fair value	$ 643.3	$ 54.5
Deposits and receivables from bds and counterparties at fair value	517.4	204.7
Physical commodities inventory at fair value	156.9	73.2
Securities Sold under Agreements to Repurchase, Fair Value of Collateral	123	19.4
Accounts pay and other accrued - fair value	0	1
Payables to b/ds and counterparties at fair value	$ 0	$ 4.8
Preferred stock - par value	$ 0.01	$ 0.01
Preferred stock - authorized	1,000,000	1,000,000
Preferred stock - issued	0	0
Preferred stock - outstanding	0	0
Common stock - par value	$ 0.01	$ 0.01
Common stock - authorized	30,000,000	30,000,000
Common stock - issued	21,030,497	20,855,243
Common stock - outstanding	18,908,540	18,733,286
Treasury stock - shares	2,121,957	2,121,957

Consolidated Income Statements

Consolidated Income Statements - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Revenues:
Sales of physical commodities	$ 26,682.4	$ 28,673.3	$ 14,112
Trading gains, net	389.1	332.2	321.2
Commission and clearing fees	356.8	283.4	224.3
Consulting, management, and account fees	71.1	65	42.2
Interest income	123.3	69.7	55.2
Total revenues	27,622.7	29,423.6	14,754.9
Cost of sales of physical commodities	26,646.9	28,639.6	14,083.9
Operating revenues	975.8	784	671
Transaction-based clearing expenses	179.7	136.3	129.9
Introducing broker commissions	133.8	113	68.9
Interest expense	80.7	42.1	28.3
Net operating revenues	581.6	492.6	443.9
Compensation and other expenses:
Compensation and benefits	337.7	295.7	263.9
Trading systems and market information	34.7	34.4	28
Occupancy and equipment rental	16.5	15.2	13.3
Professional fees	18.1	15.2	14
Travel and business development	13.8	13.3	11.5
Non-trading technology and support	13.9	11.6	7.1
Depreciation and amortization	11.6	9.8	8.2
Communications	5.4	5	4.7
Bad debts	3.1	4.3	4.4
Bad debt on physical coal	1	47	0
Other	26.3	25.9	22.3
Total compensation and other expenses	482.1	477.4	377.4
Other gains	2	0	6.2
Income from operations, before tax	101.5	15.2	72.7
Income tax expense	46	8.8	18
Net Income	$ 55.5	$ 6.4	$ 54.7
Basic earnings per share:
Net income per common share	$ 2.93	$ 0.32	$ 2.94
Diluted earnings per share:
Net income per common share	$ 2.87	$ 0.31	$ 2.90
Weighted-average number of common shares outstanding:
Basic	18,549,011	18,395,987	18,410,561
Diluted	18,934,830	18,687,354	18,625,372

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income Statement - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 55.5	$ 6.4	$ 54.7
Other comprehensive income (loss), net of tax [Abstract]
Foreign currency translation adjustment	(9)	(1.4)	(7.4)
Pension liabilities adjustment	0.3	1.2	(0.2)
Reclassification of adjustment for losses (gains) included in net income:
Periodic pension costs (included in compensation and benefits)	0.1	0.4	0.5
Income tax expense from reclassification adjustments (included in income tax expense)	0	(0.1)	0
Reclassification adjustment for losses (gains) included in net income	0.1	0.3	0.5
Other comprehensive income (loss)	(8.6)	0.1	(7.1)
Comprehensive income	$ 46.9	$ 6.5	$ 47.6

Consolidated Cash Flows Stateme

Consolidated Cash Flows Statements - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Cash flows from operating activities:
Net income	$ 55.5	$ 6.4	$ 54.7
Adjustments to reconcile net income to net cash provided by operating activities:
Bad debt on physical coal	1	47	0
Depreciation and amortization	11.6	9.8	7.8
Provision for bad debts	3.1	4.3	4.4
Deferred income taxes	22.3	(9.8)	(0.8)
Amortization and extinguishment of debt issuance costs	1	1.9	1.1
Actuarial gain on pension and postretirement benefits	(0.3)	(0.3)	0
Amortization of share-based compensation expense	6.6	6.3	5.1
(Gain) loss on sale of property and equipment	0	(0.3)	0.4
Gain on acquisition	0	0	(6.2)
Changes in operating assets and liabilities, net:
Cash, securities and other assets segregated under federal and other regulations	(928.8)	622.7	(379.9)
Change in securities purchased under agreements to resell	(464.9)	203	(285.1)
Securities borrowed	(138.8)	(79.7)	0
Deposits and receivables from broker-dealers, clearing organizations, and counterparties	408.8	(889.1)	146.6
Receivable from customers, net	(24.3)	(116.4)	97.8
Notes receivable, net	6.8	8.3	59.5
Income taxes receivable	(1.3)	0.5	8.2
Financial instruments owned, at fair value	(308.7)	(125.6)	(192.9)
Physical commodities inventory	(98.7)	(1.7)	(91)
Other assets	(3.3)	(16)	(17.4)
Accounts payable and other accrued liabilities	18.6	(19.6)	7.5
Payable to customers	520	290.9	172.2
Payable to broker-dealers, clearing organizations and counterparties	(27.8)	(124.1)	(53.8)
Income taxes payable	3.2	0.2	0.3
Securities sold under agreements to repurchase	543.7	226	159.8
Securities loaned	166.8	93.6	0
Financial instruments sold, not yet purchased, at fair value	153.9	(124.4)	273.9
Net cash provided by (used in) provided by operating activities	(74)	13.9	(27.8)
Cash flows from investing activities:
Cash paid for acquisitions, net	(3.7)	(6)	(20)
Purchase of exchange memberships and common stock	0	(0.2)	(0.1)
Sale of exchange memberships and common stock	0.8	0	0
Purchase of property and equipment	(12.5)	(16.1)	(15.4)
Net cash used in investing activities	(15.4)	(22.3)	(35.5)
Cash flows from financing activities:
Net change in payable to lenders under loans	125.8	48.2	142
Payments related to earn-outs on acquisitions	(5.5)	0	(2.9)
Repayment of senior unsecured notes	0	(45.5)	0
Payments of notes payable	(0.8)	(0.8)	(0.8)
Share repurchase	0	0	(19.5)
Debt issuance costs	(0.4)	(0.3)	(2.1)
Exercise of stock options	2.6	3.4	3.5
Payments Related to Tax Withholding for Share-based Compensation	(0.8)	0	0
Income tax benefit on stock options and awards	0	0.7	0.8
Net cash provided by financing activities	120.9	5.7	121
Effect of exchange rates on cash and cash equivalents	(4.1)	1.4	(9.6)
Net increase in cash and cash equivalents	27.4	(1.3)	48.1
Cash and cash equivalents at beginning of period	314.9	316.2	268.1
Cash and cash equivalents at end of period	342.3	314.9	316.2
Supplemental disclosure of cash flow information:
Cash paid for interest	78.9	38	26
Income taxes paid, net of cash refunds	22.2	17.1	8.5
Supplemental disclosure of non-cash investing and financing activities:
Identified intangible assets and goodwill on acquisitions	3.9	0	0
Additional consideration payable related to acquisitions	0	(0.2)	(0.4)
Acquisition of business:
Assets acquired	1.7	0	187.1
Liabilities acquired	(1.9)	0	(136)
Total net assets acquired	(0.2)	0	51.1
Escrow releases and deposits related to acquisitions	$ 0
Escrow deposits related to acquisitions		$ (5)	$ (3.4)

Consolidated Statements of Shar

Consolidated Statements of Shareholders’ Equity - USD ($) $ in Millions	Total	Common Stock [Member]	Treasury Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss [Member]
Balances at beginning of period at Sep. 30, 2015	$ 397.1	$ 0.2	$ (26.8)	$ 240.8	$ 200.4	$ (17.5)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	54.7				54.7
Other comprehensive loss	(7.1)					(7.1)
Excercise of stock options	3.5			3.5
Share-based compensation	5.1			5.1
Repurchase of stock	(19.5)		(19.5)
Repurchase of stock - adjustments to APIC				0
Balances at end of period at Sep. 30, 2016	433.8	0.2	(46.3)	249.4	255.1	(24.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	6.4				6.4
Other comprehensive loss	0.1					0.1
Excercise of stock options	3.3			3.3
Share-based compensation	6.3			6.3
Balances at end of period at Sep. 30, 2017	449.9	0.2	(46.3)	259	261.5	(24.5)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	55.5				55.5
Other comprehensive loss	(8.6)					(8.6)
Excercise of stock options	1.9			1.9
Share-based compensation	6.6			6.6
Balances at end of period at Sep. 30, 2018	$ 505.3	$ 0.2	$ (46.3)	$ 267.5	$ 317	$ (33.1)

Description of Business and Sig

Description of Business and Significant Accounting Policies (Notes)	12 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Business Description and Accounting Policies [Text Block]	Description of Business and Significant Accounting Policies INTL FCStone Inc. , a Delaware corporation, and its consolidated subsidiaries (collectively “INTL” or “the Company”), is a diversified global brokerage and financial services firm providing execution, risk management and advisory services, market intelligence and clearing services with significant asset class coverage and significant market coverage globally. The Company helps its clients to access market liquidity, maximize profits and manage risk. The Company’s revenues are derived primarily from financial products and advisory services intended to fulfill its clients’ commercial needs and provide bottom-line benefits to their businesses. The Company’s services include comprehensive risk management advisory services for commercial clients; clearing and execution of debt and equity securities, listed futures and options on futures contracts on all major securities and commodity exchanges; structured over-the-counter (“OTC”) products in a wide range of commodities; physical trading and hedging of precious and base metals and select other commodities; trading of more than 140 foreign currencies; market-making in international equities; fixed income; debt origination and asset management. The Company provides these services to a diverse group of more than 20,000 commercial and institutional clients and over 80,000 retail clients located in more than 130 countries, including commercial entities, asset managers, regional, national and introducing broker-dealers, insurance companies, brokers, institutional investors and professional traders, commercial and investment banks and government and non-governmental organizations (“NGOs”). Basis of Presentation The accompanying consolidated financial statements include the accounts of INTL FCStone Inc. and all other entities in which the Company has a controlling financial interest. All material intercompany transactions and balances have been eliminated in consolidation. Unless otherwise stated herein, all references to fiscal 2018 , fiscal 2017 , and fiscal 2016 refer to the Company’s fiscal years ended September 30. In the consolidated income statements, the total revenues reported combine gross revenues for the physical commodities business and net revenues for all other businesses. The subtotal ‘operating revenues’ in the consolidated income statements is calculated by deducting physical commodities cost of sales from total revenues. The subtotal ‘net operating revenues’ in the consolidated income statements is calculated as operating revenues less transaction-based clearing expenses, introducing broker commissions and interest expense. Transaction-based clearing expenses represent variable expenses paid to executing brokers, exchanges, clearing organizations and banks in relation to transactional volumes. Introducing broker commissions include commission paid to non-employee third parties that have introduced clients to the Company. Net operating revenues represent revenues available to pay variable compensation to risk management consultants and traders and direct non-variable expenses, as well as variable and non-variable expenses of operational and administrative employees. Use of Estimates The preparation of consolidated financial statements in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”) requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent liabilities as of the date of the financial statements and the reported amounts of revenue and expenses during the reporting period. The most significant of these estimates and assumptions relate to fair value measurements for financial instruments, revenue recognition, the provision for probable losses from bad debts, valuation of inventories, valuation of goodwill and intangible assets, and incomes taxes and contingencies. These estimates are based on management’s best knowledge of current events and actions the Company may undertake in the future. The Company reviews all significant estimates affecting the financial statements on a recurring basis and records the effect of any necessary adjustments prior to their issuance. Although these and other estimates and assumptions are based on the best available information, actual results could be materially different from these estimates. Internal Subsidiaries Consolidation Effective July 1, 2017, the Company merged its wholly-owned regulated United States (“U.S.”) subsidiary, Sterne Agee & Leach, Inc., into the wholly owned regulated U.S. subsidiary, INTL FCStone Financial Inc. (“INTL FCStone Financial”). As such, the assets, liabilities and equity of Sterne Agee & Leach, Inc. were transferred into INTL FCStone Financial. Reclassifications During the year ended September 30, 2018, the Company separately classified non-trading technology and support costs that were previously included within ‘Other’ on the consolidated income statements. Additionally, during the year ended September 30, 2018, the Company separately classified communications related expenses from trading systems and market information related costs. In performing these reclassifications, the Company has made immaterial, retrospective adjustments to conform to the current period presentation. For the years ended September 30, 2017 and 2016, ‘Other’ expenses included $11.6 million and $7.1 million , respectively, of expenses that are now included within ‘Non-trading technology and support’ on the consolidated income statements. For the years ended September 30, 2017 and 2016, ‘Trading systems and market information’ included $5.0 million and $4.7 million , respectively, of expenses that are now included within ‘Communications’ on the consolidated income statements. Foreign Currency Translation The Company’s consolidated financial statements are reported in U.S. dollars. The Company’s foreign subsidiaries maintain their records either in U.S. dollars or in certain instances the currency of the country in which they operate. The method of translating local currency financial information into U.S. dollars depends on whether the economy in which the foreign subsidiary operates has been designated as highly inflationary or not. Economies with a three-year cumulative inflation rate of more than 100% are considered highly inflationary. Assets and liabilities of foreign subsidiaries in non-highly inflationary economies are translated into U.S. dollars using rates of exchange at the balance sheet date. Translation adjustments are recorded in other comprehensive income (loss). Revenues and expense are translated at rates of exchange in effect during the year. Transaction gains and losses are recorded in earnings. Foreign subsidiaries that operate in highly inflationary countries use the U.S. dollar as their functional currency. Local currency monetary assets and liabilities are remeasured into U.S. dollars using rates of exchange as of each balance sheet date, with remeasurement adjustments and other transaction gains and losses recognized in earnings. Nonmonetary assets and liabilities do not fluctuate with changes in the local currency exchange rates to the dollar as the translated amounts for nonmonetary assets and liabilities at the end of the accounting period in which the economy becomes highly inflationary becomes the accounting basis for those assets and liabilities in the period of change and subsequent periods. Revenues and expenses are translated at rates of exchange in effect during the year. The Company operates asset management and debt trading businesses in Argentina through various wholly owned subsidiaries. Operating revenues from the Argentinean subsidiaries represented approximately 3% of the consolidated operating revenues for the year ended September 30, 2018. The operating environment in Argentina continues to present business challenges, including ongoing devaluation of the Argentine peso and significant inflation. For the year ended September 30, 2018, the Argentine peso declined approximately 139% (from 17.3 to 41.3 pesos to the U.S. dollar). Based upon inflationary data published by the International Practices Task Force of the Center for Audit Quality, the economy of Argentina became highly inflationary during the three months ended June 30, 2018. Beginning July 1, 2018, the Company has designated Argentina’s economy as highly inflationary for accounting purposes. As a result, the Company has accounted for the Argentinean entities using the U.S. dollar as their functional currency beginning in the quarter ending September 30, 2018. Argentine peso-denominated monetary assets and liabilities are remeasured at each balance sheet date to the currency exchange rate then in effect, with currency remeasurement gains and loses recognized in earnings. The translated balances for nonmonetary assets and liabilities as of June 30, 2018, became the accounting basis for those assets in the period of change and subsequent periods. As a result of Argentina’s highly inflationary status, the Company recorded translation losses through earnings of $3.4 million for the quarter ended September 30, 2018. At September 30, 2018, the Company had net monetary assets denominated in Argentine pesos of $11.6 millio n, including cash and cash equivalents of $1.4 million . At September 30, 2018, the Company had net nonmonetary assets denominated in Argentine pesos of $1.0 million . Cash and Cash Equivalents The Company considers cash held at banks and all highly liquid investments not held for trading purposes, with original or acquired maturities of 90 days or less, including certificates of deposit, to be cash and cash equivalents. Cash and cash equivalents consist of cash, foreign currency, and certificates of deposit not deposited with or pledged to exchange-clearing organizations, broker-dealers, clearing organizations or counterparties, or segregated under federal or other regulations. Certificates of deposit are stated at cost plus accrued interest, which approximates fair value, and may be withdrawn at any time at the discretion of the Company without penalty. Cash, Securities and Other Assets Segregated under Federal and other Regulations Pursuant to requirements of the Commodity Exchange Act and Commission Regulation 30.7 of the U.S. Commodity Futures Trading Commission (“CFTC”) in the U.S. and similarly in the United Kingdom (“U.K.”), pursuant to the Markets in Financial Instruments Implementing Directive 2006/73/EC underpinning the Client Asset (“CASS”) rules in the Financial Services Authority (“FSA”) handbook, funds deposited by clients relating to futures and options on futures contracts in regulated commodities must be carried in separate accounts which are designated as segregated client accounts. Additionally, in accordance with Rule 15c3-3 of the Securities Exchange Act of 1934 (“Rule 15c3-3”), the Company maintains separate accounts for the exclusive benefit of securities clients and proprietary accounts of broker dealers (“PABs”). Rule 15c3-3 requires the Company to maintain special reserve bank accounts (“SRBAs”) for the exclusive benefit of securities clients and PABs. The deposits in segregated client accounts and SRBAs are not commingled with the funds of the Company. Under the FSA’s rules, certain categories of clients may choose to opt-out of segregation. As of September 30, 2018 and 2017 , cash, securities, and other assets segregated under federal and other regulations consisted of cash held at banks of approximately $765.4 million and $464.3 million , respectively, U.S. Treasury obligations of approximately $600.4 million and $33.5 million , respectively, and commodities warehouse receipts of approximately $42.9 million and $21.0 million , respectively (see fair value measurements discussion in Note 3 ). Securities Purchased/Sold Under Agreements to Resell/Repurchase The Company enters into securities purchased under agreements to resell (reverse repurchase agreements) and securities sold under agreements to repurchase (repurchase agreements) primarily to finance financial instruments, acquire securities to cover short positions or to acquire securities for settlement. Reverse repurchase agreements and repurchase agreements are treated as collateralized financing transactions and are recorded at their contractual amounts plus accrued interest. The related interest is recorded in the 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, or may be required by 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. Securities Borrowed and Loaned The Company enters into securities borrowed and securities loaned transactions primarily to meet counterparties’ needs. Securities borrowed and securities loaned are reported as collateralized financings. Securities borrowed and securities loaned transactions are recorded at the amount of cash collateral advanced or received. The Company receives collateral generally in excess of the market value of securities loaned. The Company monitors the market value of securities borrowed and loaned on a daily basis, with additional collateral obtained or refunded as necessary. Securities borrowed and securities loaned are reported on a gross basis. Interest income and interest expense are recognized over the life of the arrangements. Deposits with and Receivables from Broker-dealers, Clearing Organizations and Counterparties, and Payables to Broker-dealers, Clearing Organizations and Counterparties As required by the regulations of the CFTC and the aforementioned FSA handbook, client funds received to margin, guarantee, and/or secure commodity futures and futures on options transactions are segregated and accounted for separately from the general assets of the Company. Deposits with broker-dealers, clearing organizations, and counterparties pertain primarily to deposits made to satisfy margin requirements on client and proprietary open futures and options on futures positions and to satisfy the requirements set by clearing exchanges for clearing membership. The Company also pledges margin deposits with various counterparties for OTC derivative contracts, and these deposits are also included in deposits with broker-dealers, clearing organizations, and counterparties. The Company also deposits cash margin with various securities clearing organizations, and these deposits are also included in deposits with broker-dealers, clearing organizations, and counterparties. Deposits with and receivables from broker-dealers, clearing organizations, and counterparties are reported gross, except where a right of offset exists. As of September 30, 2018 and 2017 , the Company had cash and cash equivalents on deposit with or pledged to broker-dealers, clearing organizations, and counterparties of approximately $1.5 billion and $2.3 billion , respectively. Deposits with and receivables from broker-dealers, clearing organizations, and counterparties also include securities pledged to exchange-clearing organizations as collateral in lieu of cash margin by the Company on behalf of clients and client-owned securities that are pledged directly. It is the Company’s practice to include client-owned securities on its consolidated balance sheets, as the rights to those securities have been transferred to the Company under the terms of the futures trading agreements. Securities pledged primarily include U.S. Treasury obligations, foreign government obligations, and certain exchange-traded funds (“ETFs”). Securities that are not client-owned are adjusted to fair value with associated changes in unrealized gains or losses recorded through current period earnings. For client-owned securities, the change in fair value is offset against the payable to clients with no impact recognized in the consolidated income statements. The fair value of these securities included within deposits with and receivables from broker-dealers, clearing organizations, and counterparties was $785.8 million and $251.4 million as of September 30, 2018 and 2017 , respectively. Management has considered guidance required by Accounting Standards Codification (“ASC”) 860 - Transfers and Servicing as it relates to securities pledged by clients to margin their accounts within the FCM Division of INTL FCStone Financial. Based on a review of the agreements with the client, management believes the transferor surrenders control over those assets because: (a) the transferred assets have been isolated from the transferor—put presumptively beyond the reach of the transferor and its creditors, even in bankruptcy or other receivership, (b) each transferee has the right to pledge or exchange the assets (or beneficial interests) it received, and no condition both constrains the transferee (or holder) from taking advantage of its right to pledge or exchange and provides more than a trivial benefit to the transferor and (c) the transferor does not maintain effective control over the transferred assets through either (1) an agreement that both entitles and obligates the transferor to repurchase or redeem them before their maturity or (2) the ability to unilaterally cause the holder to return specific assets, other than through a cleanup call. Under this guidance, the Company reflects the client collateral assets and corresponding liabilities in the Company’s consolidated balance sheets as of September 30, 2018 and 2017 . In addition to cash margin, deposits with and receivables from broker-dealers, clearing organizations, and counterparties include guaranty deposits with exchange-clearing organizations. The guaranty deposits are held by the clearing organization for use in potential default situations by one or more members of the clearing organization. The guaranty deposits may be applied to the Company’s obligations to the clearing organization, or to the clearing organization’s obligations to other clearing members or third parties. The Company maintains client omnibus and proprietary accounts with other counterparties, and the equity balances in those accounts along with any margin cash or securities deposited with the carrying broker are included in deposits with and receivables from broker-dealers, clearing organizations, and counterparties. Deposits with and receivables from broker-dealers, clearing organizations, and counterparties also include amounts due from or due to exchange-clearing organizations for daily variation settlements on open futures and options on futures positions. The variation settlements due from or due to exchange-clearing organizations are paid in cash on the following business day and represent the settlement of futures positions. Deposits with and receivables from broker-dealers, clearing organizations and counterparties, and payables to broker-dealers, clearing organizations and counterparties also include amounts related to the value of clients cross-currency payment transactions related to the Global Payments segment. These amounts arise due to a clearing period before the funds are received and payments are made, which usually is one to two business days. Deposits with and receivables from broker-dealers, clearing organizations, and counterparties also includes amounts due from exchange-clearing organizations for unrealized gains and losses associated with clients’ options on futures contracts. See discussion in the Financial Instruments section below for additional information on the Company’s accounting policies for derivative contracts. For client-owned derivative contracts, the fair value is offset against the payable to clients with no impact recognized on the consolidated income statements. Receivable from and Payable to Clients Receivable from clients, net of the allowance for doubtful accounts, include the total of net deficits in individual exchange-traded futures and OTC derivative trading accounts carried by the Company. Client deficits arise from realized and unrealized trading losses on client futures, options on futures, swaps and forwards and amounts due on cash and margin transactions. Client deficit accounts are reported gross of client accounts that contain net credit or positive balances, except where a right of offset exists. Net deficits in individual futures exchange-traded and OTC derivative trading accounts include both secured and unsecured deficit balances due from clients as of the balance sheet date. Secured deficit amounts are backed by U.S. Treasury obligations and commodity warehouse receipts. These U.S Treasury obligations and commodity warehouse receipts are not netted against the secured deficit amounts, as the conditions for right of setoff have not been met. Receivable from clients, net also includes the net amounts receivable from securities clients in connection with the settlement of regular-way cash securities, margin loans to clients, and client cash debits. It is the Company’s policy to report margin loans and payables that arise due to positive cash flows in the same client’s accounts on a net basis when the conditions for netting as specified in U.S. GAAP are met. Clients’ securities transactions cleared by the Company are recorded on a settlement date basis. Securities cleared by the Company and pledged to the Company as a condition of the custodial clearing arrangements are owned by the clients, including those that collateralize margin or other similar transactions, and are not reflected on the consolidated balance sheets as the Company does not have title to, or beneficial interests, in those assets. In the event of uncompleted transactions on settlement date, the Company records corresponding receivables and payables, respectively. The carrying value of the receivables and payables approximates fair value due to their short-term nature. Payable to clients represent the total of client accounts with credit or positive balances. Client accounts are used primarily in connection with commodity, foreign exchange, precious metals, and securities transactions and include gains and losses on open trades as well as securities and cash margin deposits made as required by the Company, the exchange-clearing organizations or other clearing organizations. Client accounts with credit or positive balances are reported gross of client deficit accounts, except where a right of offset exists. Receivable from and payables to clients also include amounts related to the value of clients cross-currency payment transactions related to the Global Payments segment. These amounts arise due to a clearing period before the funds are received and payments are made, which usually is one to two business days. The future collectability of receivables from clients can be impacted by the Company’s collection efforts, the financial stability of its clients, and the general economic climate in which it operates. The Company evaluates accounts that it believes may become uncollectible on a specific identification basis, through reviewing daily margin deficit reports, the historical daily aging of the receivables, and by monitoring the financial strength of its clients. The Company may unilaterally close client trading positions in certain circumstances. In addition, to evaluate client margining and collateral requirements, client positions are stress tested regularly and monitored for excessive concentration levels relative to the overall market size. Furthermore, in certain instances, the Company is indemnified, and able to charge back, introducing broker-dealers for bad debts incurred by their clients. The Company generally charges off an outstanding receivable balance when all economic means of recovery have been exhausted. That determination considers information such as the occurrence of significant changes in the client’s financial position such that the client can no longer pay the obligation, or that the proceeds from collateral will not be sufficient to pay the balance. Notes Receivable Accrual of commodity financing income on any note is discontinued when, in the opinion of management, there is reasonable doubt as to the timely collectability of interest or principal. Nonaccrual notes are returned to an accrual status when, in the opinion of management, the financial position of the borrower indicates there is no longer any reasonable doubt as to the timely payment of principal and interest. The Company records a charge against earnings for notes receivable losses when management believes that the collection of outstanding principal is not probable. Physical Commodities Inventory Inventories of certain agricultural commodities are carried at net realizable value, which approximates fair value less disposal costs. The agricultural commodities inventories have reliable, readily determinable and realizable market prices, have relatively predictable and insignificant costs of disposal and are available for immediate delivery. Changes in the fair values of these agricultural commodities inventories are included as a component of ‘cost of physical commodities sold’ in the consolidated income statements. Inventories of energy related products are valued at the lower of cost or net realizable value. Inventories of precious metals held by subsidiaries that are not broker-dealers are valued at the lower of cost or net realizable value, using the weighted-average price and first-in first-out costing method. Precious metals inventory held by INTL FCStone Ltd, a U.K. based broker-dealer subsidiary, is measured at fair value, with changes in fair value included as a component of ‘trading gains, net’ in the consolidated income statements. Property and Equipment Property and equipment is stated at cost, net of accumulated depreciation and amortization and depreciated using the straight-line method over the estimated useful lives of the assets. Leasehold improvements are amortized on a straight-line basis over the estimated useful life of the improvement or the term of the lease, whichever is shorter. Certain costs of software developed or obtained for internal use are capitalized and amortized over the estimated useful life of the software. Expenditures for maintenance, repairs, and minor replacements are charged against earnings, as incurred. Expenditures that increase the value or productive capacity of assets are capitalized. When property and equipment are retired, sold, or otherwise disposed of, the asset’s carrying amount and related accumulated depreciation are removed from the accounts and any gain or loss is included in earnings. Goodwill and Identifiable Intangible Assets Goodwill is the cost of acquired companies in excess of the fair value of identifiable net assets at the acquisition date. Goodwill is not subject to amortization, but rather is evaluated for impairment at least annually. The Company evaluates its goodwill for impairment at the fiscal year end (or more frequently if indicators of potential impairment exist) in accordance with ASC 350 - Intangibles - Goodwill and Other . Goodwill impairment is determined by comparing the estimated fair value of a reporting unit with its respective carrying value. If the estimated fair value exceeds the carrying value, goodwill at the reporting unit level is not deemed to be impaired. However, if the estimated fair value is below carrying value, further analysis is required to determine the amount of the impairment. This further analysis involves assigning tangible assets and liabilities, identified intangible assets and goodwill to reporting units and comparing the fair value of each reporting unit to its carrying amount. In the course of the evaluation of the potential impairment of goodwill, the Company may perform either a qualitative or a quantitative assessment. The Company’s qualitative assessment of potential impairment may result in the determination that a quantitative impairment analysis is not necessary. Under this elective process, the Company assesses qualitative factors to determine whether the existence of events or circumstances leads the Company to determine that it is more likely than not that the fair value of a reporting unit is less than its carrying amount. If after assessing the totality of events or circumstances, the Company determines it is more likely than not that the fair value of a reporting unit is greater than its carrying amount, then performing a quantitative analysis is not required. However, if the Company concludes otherwise, then the Company performs a quantitative impairment analysis. If the Company either chooses not to perform a qualitative assessment, or the Company chooses to perform a qualitative assessment but is unable to qualitatively conclude that no impairment has occurred, then the Company performs a quantitative evaluation. In the case of a quantitative assessment, the Company estimates the fair value of the reporting unit which the goodwill that is subject to the quantitative analysis is associated (generally defined as the businesses for which financial information is available and reviewed regularly by management) and compares it to the carrying value. If the estimated fair value of a reporting unit is less than its carrying value, the Company estimates the fair value of all assets and liabilities of the reporting unit, including goodwill. If the carrying value of the reporting unit’s goodwill is greater than the estimated fair value, an impairment charge is recognized for the excess. The fair value of the Company’s reporting units exceeded their respective carrying values under the first step of the quantitative assessment and no impairment charges were recorded for any of the periods presented. Identifiable intangible assets subject to amortization are amortized using the straight-line method over their estimated period of benefit, ranging from two to twenty years. Identifiable intangible assets are tested for impairment whenever events or changes in circumstances suggest that an asset’s or asset group’s carrying value may not be fully recoverable. Residual value is presumed to be zero for all identifiable intangible assets. Financial Instruments Owned and Sold, Not Yet Purchased Financial instruments owned and sold, not yet purchased, at fair value consist of financial instruments carried at fair value on a recurring basis or amounts that approximate fair value, with related realized and unrealized gains and losses recognized in current period earnings. Realized and unrealized gains and losses on financial instruments owned and sold, not yet purchased, are included in ‘Trading gains, net’ and ‘Cost of sales of physical commodities’ in the consolidated income statements. The fair value of a financial instrument is the amount at which the instrument could be exchanged in a current transaction between willing parties, other than in a forced or liquidation sale. Financial instruments owned and sold, not yet purchased are comprised primarily of the financial instruments held by the Company’s broker-dealer subsidiaries and the Company’s over-the-counter (“OTC”) derivative swap dealer. Financial instruments owned and financial instruments sold, not yet purchased, includes trading securities that the Company holds as a principal. The Company has not classified any financial instruments owned or sold, not yet purchased, as available-for-sale or held-to-maturity. Financial instruments owned and sold, not yet purchased includes derivative instruments that the Company holds as a principal which are primarily transacted on an OTC basis. As a derivatives dealer, the Company utilizes derivative instruments to manage exposures to foreign currency, commodity price and interest rate risks for the Company and its clients. The Company’s objectives for holding derivatives include reducing, eliminating, and efficiently managing the economic impact of these exposures as effectively as possible. The Company’s derivative instruments also include forward purchase and sale commitments for the physical delivery of agricultural and energy related commodities in a future period. Contracts t

Earnings per Share (Notes)

Earnings per Share (Notes)	12 Months Ended
	Sep. 30, 2018
Earnings Per Share [Abstract]
Earnings Per Share [Text Block]	Earnings per Share The Company presents basic and diluted earnings per share (“EPS”) using the two-class method which requires all outstanding unvested share-based payment awards that contain rights to non-forfeitable dividends and therefore participate in undistributed earnings with common stockholders be included in computing earnings per share. Under the two-class method, net income is reduced by the amount of dividends declared in the period for each class of common stock and participating security. The remaining undistributed earnings are then allocated to common stock and participating securities, based on their respective rights to receive dividends. Restricted stock awards granted to certain employees and directors contain non-forfeitable rights to dividends at the same rate as common stock, and are considered participating securities. Basic EPS has been computed by dividing net income by the weighted-average number of common shares outstanding. The following is a reconciliation of the numerator and denominator of the diluted net income per share computations for the periods presented below. Year Ended September 30, (in millions, except share amounts) 2018 2017 2016 Numerator: Net income $ 55.5 $ 6.4 $ 54.7 Less: Allocation to participating securities (0.9 ) (0.1 ) (1.0 ) Net income allocated to common stockholders $ 54.6 $ 6.3 $ 53.7 Denominator: Weighted average number of: Common shares outstanding 18,549,011 18,395,987 18,410,561 Dilutive potential common shares outstanding: Share-based awards 385,819 291,367 214,811 Diluted shares outstanding 18,934,830 18,687,354 18,625,372 The dilutive effect of share-based awards is reflected in diluted net income per share by application of the treasury stock method, which includes consideration of unamortized share-based compensation expense. Options to purchase 92,627 , 230,135 and 910,060 shares of common stock for fiscal years ended September 30, 2018, 2017, and 2016 , respectively, were excluded from the calculation of diluted earnings per share because they would have been anti-dilutive.

Assets and Liabilities, at Fair

Assets and Liabilities, at Fair Value (Notes)	12 Months Ended
	Sep. 30, 2018
Assets and Liabilities, at Fair Value [Abstract]
Fair Value Disclosures [Text Block]	Assets and Liabilities, at Fair Value Fair value is defined by U.S. GAAP as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between willing market participants on the measurement date. Fair value is a market-based measure considered from the perspective of a market participant rather than an entity-specific measure. Therefore, even when market assumptions are not readily available, the Company is required to develop a set of assumptions that reflect those that market participants would use in pricing the asset or liability at the measurement date. The Company uses prices and inputs that are current as of the measurement date, including periods of market dislocation. In periods of market dislocation, the observability of prices and inputs may be reduced for many securities. This condition could cause a security to be reclassified to a lower level within the fair value hierarchy. The Company has designed independent price verification controls and periodically performs such controls to ensure the reasonableness of such values. In accordance with FASB ASC 820, Fair Value Measurement, the Company groups its assets and liabilities measured at fair value in three levels based on the markets in which the assets and liabilities are traded and the reliability of the assumptions used to determine fair value. These levels are: Level 1 - Valuation is based upon unadjusted quoted prices in active markets that are accessible at the measurement date for identical, unrestricted assets or liabilities. Level 1 consists of financial assets and liabilities whose fair values are estimated using quoted market prices. Level 2 - Valuation is based upon quoted prices for identical or similar assets or liabilities in markets that are less active, that is, markets in which there are few transactions for the asset or liability that are observable for substantially the full term. Included in Level 2 are those financial assets and liabilities for which fair values are estimated using models or other valuation methodologies. These models are primarily industry-standard models that consider various observable inputs, including time value, yield curve, volatility factors, observable current market and contractual prices for the underlying financial instruments, as well as other relevant economic measures. Level 3 - Valuation is generated from prices or valuation techniques that require inputs that are both significant to the fair value measurement and unobservable (i.e., supported by little or no market activity). Level 3 comprises financial assets and liabilities whose fair value is estimated based on internally developed models or methodologies utilizing significant inputs that are not readily observable from objective sources. Financial and nonfinancial assets and liabilities are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1 measurements) and the lowest priority to unobservable inputs (Level 3 measurements). A market is active if there are sufficient transactions on an ongoing basis to provide current pricing information for the asset or liability, pricing information is released publicly, and price quotations do not vary substantially either over time or among market makers. Observable inputs reflect the assumptions market participants would use in pricing the asset or liability developed based on market data obtained from sources independent of the reporting entity. The guidance requires the Company to consider counterparty credit risk of all parties of outstanding derivative instruments that would be considered by a market participant in the transfer or settlement of such contracts (exit price). The Company’s exposure to credit risk on derivative financial instruments relates to the portfolio of OTC derivative contracts as all exchange-traded contracts held can be settled on an active market with a credit guarantee from the respective exchange. The Company requires each counterparty to deposit margin collateral for all OTC instruments and is also required to deposit margin collateral with counterparties. The Company has assessed the nature of these deposits and used its discretion to adjust each based on the underlying credit considerations for the counterparty and determined that the collateral deposits minimize the exposure to counterparty credit risk in the evaluation of the fair value of OTC instruments as determined by a market participant. Fair value of financial and nonfinancial assets and liabilities that are carried on the Consolidated Balance Sheets at fair value on a recurring basis Cash and cash equivalents reported at fair value on a recurring basis includes certificates of deposit, which are stated at cost plus accrued interest, which approximates fair value. Cash, securities and other assets segregated under federal and other regulations reported at fair value on a recurring basis include the value of pledged investments, primarily U.S. Treasury obligations and commodities warehouse receipts. Deposits with and receivables from broker-dealers, clearing organizations and counterparties and payable to clients and broker-dealers, clearing organizations and counterparties includes the fair value of pledged investments, primarily U.S. Treasury obligations and foreign government obligations. These balances also include the fair value of exchange-traded options on futures and OTC forwards, swaps, and options. Financial instruments owned and sold, not yet purchased include the fair value of equity securities, which includes common, preferred, and foreign ordinary shares, American Depository Receipts (“ADRs”), Global Depository Receipts (“GDRs”), and exchange-traded funds (“ETFs”), corporate and municipal bond, U.S. Treasury obligations, U.S. government agency obligations, foreign government obligations, agency mortgage-backed obligations, asset-backed obligations, derivative financial instruments, commodities warehouse receipts, exchange firm common stock, and mutual funds and investments in managed funds. The fair value of exchange firm common stock is determined by quoted market prices, and the fair value of exchange memberships is determined by recent sale transactions. Cash equivalents, securities, commodities warehouse receipts, physical commodities inventory, derivative financial instruments and contingent liabilities are carried at fair value, on a recurring basis, and are classified and disclosed into three levels in the fair value hierarchy. The following section describes the valuation methodologies used by the Company to measure classes of financial instruments at fair value and specifies the level within the fair value hierarchy where various financial instruments are classified. The Company uses quoted prices in active markets, where available, and classifies such instruments within Level 1 of the fair value hierarchy. Examples include U.S. Treasury obligations, foreign government obligations, commodities warehouse receipts, certain equity securities traded in active markets, physical precious metals inventory, equity investments in exchange firms, investments in managed funds, as well as options on futures contracts traded on national exchanges. The fair value of exchange memberships is determined by recent sale transactions and is included within Level 1. When instruments are traded in secondary markets and observable prices are not available for substantially the full term, the Company generally relies on internal valuation techniques or prices obtained from third-party pricing services or brokers or a combination thereof, and accordingly, classified these instruments as Level 2. Examples include corporate and municipal bonds, U.S. government agency obligations, agency-mortgage backed obligations, asset-backed obligations, certain equity securities traded in less active markets, OTC commodity, interest rate, and foreign exchange forwards, swaps, and options, and OTC firm purchase and sale commitments related to the Company’s agricultural and energy commodities. Certain derivatives without a quoted price in an active market and derivatives executed OTC are valued using internal valuation techniques, including pricing models which utilize significant inputs observable to market participants. The valuation techniques and inputs depend on the type of derivative and the nature of the underlying instrument. The key inputs depend upon the type of derivative and the nature of the underlying instrument and include interest yield curves, foreign exchange rates, commodity prices, volatilities and correlation. These derivative instruments are included within Level 2 of the fair value hierarchy. Physical commodities inventory includes precious metals that are a part of the trading activities of a regulated broker-dealer subsidiary and is recorded at net realizable value using exchange-quoted prices. Physical commodities inventory also includes agricultural commodities that are a part of the trading activities of a non-broker dealer subsidiary and are also recorded at net realizable value using exchange-quoted prices. The fair value of precious metals physical commodities inventory is based upon unadjusted exchange-quoted prices and is, therefore, classified within Level 1 of the fair value hierarchy. The fair value of agricultural physical commodities inventory and the related OTC firm sale and purchase commitments are generally based upon exchange-quoted prices, adjusted for basis or differences in local markets, broker or dealer quotations or market transactions in either listed or OTC markets. Exchange-quoted prices are adjusted for location and quality because the exchange-quoted prices for agricultural and energy related products represent contracts that have standardized terms for commodity, quantity, future delivery period, delivery location, and commodity quality or grade. The basis or local market adjustments are observable inputs or have an insignificant impact on the measurement of fair value and, therefore, the agricultural physical commodities inventory as well as the related OTC forward firm sale and purchase commitments have been included within Level 2 of the fair value hierarchy. With the exception of certain derivative instruments, financial instruments owned and sold are primarily valued using third party pricing sources. Third party vendors compile prices from various sources and often apply matrix pricing for similar securities when no prices are observable. The Company reviews the pricing methodologies provided by the various vendors in order to determine if observable market information is being used, versus unobservable inputs. When evaluating the propriety of an internal trader price compared with vendor prices, considerations include the range and quality of vendor prices. Trader or broker prices are used to ensure the reasonableness of a vendor price; however valuing financial instruments involves judgments acquired from knowledge of a particular market. If a trader asserts that a vendor or market price is not reflective of market value, justification for using the trader or broker price, including recent sales activity where possible, must be provided to and approved by the appropriate levels of management. Financial instruments owned and sold that are valued using third party pricing sources are included within either Level 1 or Level 2 of the fair value hierarchy based upon the observability of the inputs used and the level of activity in the market. Level 3 comprises financial assets and liabilities whose fair value is estimated based on internally developed models or methodologies utilizing significant inputs that are not readily observable from objective sources. As of September 30, 2017, included in Level 3 were certain equity securities and contingent liabilities. Level 3 assets and liabilities were valued using an income approach based upon management developed discounted cash flow projections, which are an unobservable input. The Company had no Level 3 assets and liabilities as of September 30, 2018, as the balances were settled during the year ended September 30, 2018. The fair value estimates presented herein are based on pertinent information available to management as of September 30, 2018 and 2017 . Although management is not aware of any factors that would significantly affect the estimated fair value amounts, such amounts have not been comprehensively revalued for purposes of these financial statements since that date and current estimates of fair value may differ significantly from the amounts presented herein. The following tables set forth the Company’s financial and nonfinancial assets and liabilities accounted for at fair value, on a recurring basis, as of September 30, 2018 and September 30, 2017 by level in the fair value hierarchy. There were no assets or liabilities that were measured at fair value on a nonrecurring basis as of September 30, 2018 and 2017 . September 30, 2018 (in millions) Level 1 Level 2 Level 3 Netting (1) Total Assets: Certificates of deposit $ 3.8 $ — $ — $ — $ 3.8 Unrestricted cash equivalents - certificates of deposit 3.8 — — — 3.8 Commodities warehouse receipts 42.9 — — — 42.9 U.S. Treasury obligations 600.4 — — — 600.4 Securities and other assets segregated under federal and other regulations 643.3 — — — 643.3 U.S. Treasury obligations 778.4 — — — 778.4 “To be announced” (TBA) and forward settling securities — 5.0 — (2.1 ) 2.9 Foreign government obligations 7.7 — — — 7.7 Derivatives 7,495.9 19.6 — (7,787.1 ) (271.6 ) Deposits with and receivables from broker-dealers, clearing organizations and counterparties 8,282.0 24.6 — (7,789.2 ) 517.4 Equity securities 71.2 3.0 — — 74.2 Corporate and municipal bonds — 79.1 — — 79.1 U.S. Treasury obligations 120.1 — — — 120.1 U.S. government agency obligations — 472.9 — — 472.9 Foreign government obligations 6.4 — — — 6.4 Agency mortgage-backed obligations — 1,022.5 — — 1,022.5 Asset-backed obligations — 42.9 — — 42.9 Derivatives 0.8 514.6 — (329.3 ) 186.1 Commodities leases — 29.5 — (11.8 ) 17.7 Commodities warehouse receipts 16.4 — — — 16.4 Exchange firm common stock 10.2 — — — 10.2 Mutual funds and other 6.3 — — — 6.3 Financial instruments owned 231.4 2,164.5 — (341.1 ) 2,054.8 Physical commodities inventory 42.1 114.8 — — 156.9 Total assets at fair value $ 9,202.6 $ 2,303.9 $ — $ (8,130.3 ) $ 3,376.2 Liabilities: Accounts payable and other accrued liabilities - contingent liabilities $ — $ — $ — $ — $ — TBA and forward settling securities — 2.1 — (2.1 ) — Derivatives 7,809.3 11.6 — (7,820.9 ) — Payables to broker-dealers, clearing organizations and counterparties 7,809.3 13.7 — (7,823.0 ) — Equity securities 51.1 0.4 — — 51.5 Corporate and municipal bonds — 20.1 — — 20.1 U.S. Treasury obligations 484.8 — — — 484.8 U.S government agency obligations — 57.2 — — 57.2 Agency mortgage-backed obligations — 0.2 — — 0.2 Derivatives — 688.0 — (494.6 ) 193.4 Commodities leases — 75.5 — (16.2 ) 59.3 Financial instruments sold, not yet purchased 535.9 841.4 — (510.8 ) 866.5 Total liabilities at fair value $ 8,345.2 $ 855.1 $ — $ (8,333.8 ) $ 866.5 (1) Represents cash collateral and the impact of netting across the levels of the fair value hierarchy. Netting among positions classified within the same level are included in that level. September 30, 2017 (in millions) Level 1 Level 2 Level 3 Netting (1) Total Assets: Certificate of deposits $ 3.8 $ — $ — $ — $ 3.8 Unrestricted cash equivalents - certificates of deposits 3.8 — — — 3.8 Commodities warehouse receipts 21.0 — — — 21.0 U.S. Treasury obligations 33.5 — — — 33.5 Securities and other assets segregated under federal and other regulations 54.5 — — — 54.5 Foreign government obligations — 6.4 — — 6.4 U.S. Treasury obligations 244.7 — — — 244.7 TBA and forward settling securities — 8.8 — — 8.8 Derivatives 2,608.6 289.1 — (2,952.9 ) (55.2 ) Deposits and receivables from broker-dealers, clearing organizations and counterparties 2,853.3 304.3 — (2,952.9 ) 204.7 Equity securities 40.4 4.6 0.1 — 45.1 Corporate and municipal bonds 28.2 0.9 — — 29.1 U.S. Treasury obligations 60.0 — — — 60.0 U.S. government agency obligations — 368.9 — — 368.9 Foreign government obligations — 10.2 — — 10.2 Agency mortgage-backed obligations — 920.9 — — 920.9 Asset-backed obligations — 47.3 — — 47.3 Derivatives 1.3 1,413.4 — (1,252.6 ) 162.1 Commodities leases — 174.1 — (138.7 ) 35.4 Commodities warehouse receipts 38.5 — — — 38.5 Exchange firm common stock 8.3 — — — 8.3 Mutual funds and other 6.0 — — — 6.0 Financial instruments owned 182.7 2,940.3 0.1 (1,391.3 ) 1,731.8 Physical commodities inventory 73.2 — — — 73.2 Total assets at fair value $ 3,167.5 $ 3,244.6 $ 0.1 $ (4,344.2 ) $ 2,068.0 Liabilities: Accounts payable and other accrued liabilities - contingent liabilities $ — $ — $ 1.0 $ — $ 1.0 TBA and forward settling securities — 4.9 — (0.1 ) 4.8 Derivatives 2,476.2 292.8 — (2,769.0 ) — Payable to broker-dealers, clearing organizations and counterparties - derivatives 2,476.2 297.7 — (2,769.1 ) 4.8 Equity securities 44.0 0.9 — — 44.9 Corporate and municipal bonds 0.3 — — — 0.3 U.S. Treasury obligations 285.9 — — — 285.9 U.S government agency obligations — 27.9 — — 27.9 Agency mortgage-backed obligations — 0.1 — — 0.1 Derivatives — 1,427.2 — (1,110.2 ) 317.0 Commodities leases — 191.1 — (149.6 ) 41.5 Financial instruments sold, not yet purchased 330.2 1,647.2 — (1,259.8 ) 717.6 Total liabilities at fair value $ 2,806.4 $ 1,944.9 $ 1.0 $ (4,028.9 ) $ 723.4 (1) Represents cash collateral and the impact of netting across the levels of the fair value hierarchy. Netting among positions classified within the same level are included in that level. Realized and unrealized gains and losses are included in ‘trading gains, net’, ‘interest income’, and ‘cost of sales of physical commodities’ in the consolidated income statements. Information on Level 3 Financial Assets and Liabilities The following tables set forth a summary of changes in the fair value of the Company’s Level 3 financial assets and liabilities during the fiscal years ended September 30, 2018 and 2017 , including a summary of unrealized gains (losses) during the fiscal year ended on the Company’s Level 3 financial assets and liabilities held during the periods. Level 3 Financial Assets and Financial Liabilities (in millions) Balances at Realized gains Unrealized Purchases/ Settlements Transfers in Balances at Assets: Equity securities $ 0.1 $ — $ (0.1 ) $ — $ — $ — $ — (in millions) Balances at Realized (gains) Remeasurement Acquisitions Settlements Transfers in Balances at Liabilities: Contingent liabilities $ 1.0 $ — $ — $ — $ (1.0 ) $ — $ — Level 3 Financial Assets and Financial Liabilities (in millions) Balances at Realized gains Unrealized Purchases/ Settlements Transfers in Balances at Assets: Equity securities $ 0.2 $ — $ (0.1 ) $ — $ — $ — $ 0.1 Corporate and municipal bonds 3.0 — — — (3.0 ) — — $ 3.2 $ — $ (0.1 ) $ — $ (3.0 ) $ — $ 0.1 (in millions) Balances at Realized (gains) Remeasurement Acquisitions Settlements Transfers in Balances at Liabilities: Contingent liabilities $ 0.8 $ — $ 0.2 $ — $ — $ — $ 1.0 The Company had debentures issued by a single asset owning company of Suriwongse Hotel located in Chiang Mai, Thailand. As of September 30, 2016, the Company’s investment in the hotel was $3.0 million , and was included within the corporate and municipal bonds classification in the Level 3 financial assets and financial liabilities table. The Company classified its investment in the hotel within Level 3 of the fair value hierarchy because the fair value was determined using significant unobservable inputs, which included projected cash flows. These cash flows were discounted employing present value techniques. In December 2016, the Company sold the debentures and collected an amount approximating their carrying value. The Company was required to make additional future cash payments based on certain financial performance measures of an acquired business. The Company was required to remeasure the fair value of the contingent consideration on a recurring basis. As of September 30, 2017, the Company had classified its liability for the contingent consideration within Level 3 of the fair value hierarchy because the fair value was determined using significant unobservable inputs, which included projected cash flows. These cash flows were discounted employing present value techniques in arriving at fair value. The fair value of the contingent consideration increased by $0.1 million during the year ended September 30, 2017, with the corresponding amount classified as ‘other’ in the consolidated income statement. The contingency period for the contingent consideration ended as of December 31, 2017, and the accrued balance of $1.0 million was paid during the year ended September 30, 2018. The value of an exchange-traded derivative contract is equal to the unrealized gain or loss on the contract determined by marking the contract to the current settlement price for a like contract on the valuation date of the contract. A settlement price may not be used if the market makes a limit move with respect to a particular derivative contract or if the securities underlying the contract experience significant price fluctuations after the determination of the settlement price. When a settlement price cannot be used, derivative contracts will be valued at their fair value as determined in good faith pursuant to procedures adopted by management of the Company. The Company has classified equity investments in exchange firms’ common stock not pledged for clearing purposes as trading securities. The investments are recorded at fair value, with unrealized gains and losses recorded, net of taxes, included in earnings. As of September 30, 2018 , the cost and fair value of the equity investments in exchange firms is $3.7 million and $10.2 million , respectively. As of September 30, 2017 , the cost and fair value of the equity investments in exchange firms was $3.9 million and $8.3 million , respectively. Additional disclosures about the fair value of financial instruments that are not carried on the Consolidated Balance Sheets at fair value Many, but not all, of the financial instruments that the Company holds are recorded at fair value in the Consolidated Balance Sheets. The following represents financial instruments in which the ending balance at September 30, 2018 and 2017 was not carried at fair value in accordance with U.S. GAAP on our Consolidated Balance Sheets: Short-term financial instruments: The carrying value of short-term financial instruments, including cash and cash equivalents, cash segregated under federal and other regulations, securities purchased under agreements to re-sell and securities sold under agreements to re-purchase, and securities borrowed and loaned are recorded at amounts that approximate the fair value of these instruments due to their short-term nature and level of collateralization. These financial instruments generally expose us to limited credit risk and have no stated maturities or have short-term maturities and carry interest rates that approximate market rates. Under the fair value hierarchy, cash and cash equivalents and cash segregated under federal and other regulations are classified as Level 1. Securities purchased under agreements to re-sell and securities sold under agreements to re-purchase, and securities borrowed and loaned are classified as Level 2 under the fair value hierarchy as they are generally overnight and are collateralized by common stock, U.S. Treasury obligations, U.S. government agency obligations, agency mortgage-backed obligations, and asset-backed obligations. Receivables and other assets: R eceivables from broker-dealers, clearing organizations, and counterparties, receivables from clients, net, notes receivables, net and certain other assets are recorded at amounts that approximate fair value due to their short-term nature and are classified as Level 2 under the fair value hierarchy. Payables: P ayables to clients and payables to brokers-dealers, clearing organizations, and counterparties are recorded at amounts that approximate fair value due to their short-term nature and are classified as Level 2 under the fair value hierarchy. Lender under loans : Payables to lenders under loans carry variable rates of interest and thus approximate fair value and are classified as Level 2 under the fair value hierarchy.

Financial Instruments with Off-

Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk (Notes)	12 Months Ended
	Sep. 30, 2018
Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk [Abstract]
Derivative Instruments and Hedging Activities Disclosure [Text Block]	Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk The Company is party to certain financial instruments with off-balance sheet risk in the normal course of its business. The Company has sold financial instruments that it does not currently own and will therefore be obliged to purchase such financial instruments at a future date. The Company has recorded these obligations in the consolidated financial statements as of September 30, 2018 at the fair values of the related financial instruments. The Company will incur losses if the fair value of the underlying financial instruments increases subsequent to September 30, 2018 . The total of $866.5 million as of September 30, 2018 includes $193.4 million for derivative contracts, which represent a liability to the Company based on their fair values as of September 30, 2018 . Derivatives The Company utilizes derivative products in its trading capacity as a dealer in order to satisfy client needs and mitigate risk. The Company manages risks from both derivatives and non-derivative cash instruments on a consolidated basis. The risks of derivatives should not be viewed in isolation, but in aggregate with the Company’s other trading activities. The Company’s derivative positions are included in the consolidating balance sheets in ‘deposits with and receivables from broker-dealers, clearing organizations, and counterparties’, ‘financial instruments owned and sold, not yet purchased, at fair value’ and ‘payables to broker-dealers, clearing organizations and counterparties’. The Company employs an interest rate risk management strategy using derivative financial instruments in the form of interest rate swaps as well as outright purchases of medium-term U.S. Treasury notes to manage a portion of the aggregate interest rate position. The Company’s objective when using interest rate swaps under the strategy, is to invest certain amounts of customer deposits in high quality, short-term investments and swap the resulting variable interest earnings into medium-term interest earnings. When used, the risk mitigation of these interest rate swaps are not within the documented hedging designation requirements of the Derivatives and Hedging Topic of the ASC, and as a result are recorded at fair value, with changes in the fair value of the interest rate swaps recorded within 'trading gains, net' in the consolidated income statements. Currently, the Company holds no U.S. Treasury notes or interest rate swap derivative contracts as part of this strategy. Listed below are the fair values of the Company’s derivative assets and liabilities as of September 30, 2018 and 2017 . Assets represent net unrealized gains and liabilities represent net unrealized losses. September 30, 2018 September 30, 2017 (in millions) Assets (1) Liabilities (1) Assets (1) Liabilities (1) Derivative contracts not accounted for as hedges: Exchange-traded commodity derivatives $ 2,455.7 $ 2,499.3 $ 2,094.2 $ 1,975.0 OTC commodity derivatives 207.0 369.9 1,084.0 1,110.3 Exchange-traded foreign exchange derivatives 49.8 37.2 66.0 52.0 OTC foreign exchange derivatives 302.5 303.9 618.5 609.8 Exchange-traded interest rate derivatives 449.3 478.7 228.4 203.6 OTC interest rate derivatives 24.8 25.9 — — Exchange-traded equity index derivatives 4,541.8 4,794.0 221.3 245.4 TBA and forward settling securities 5.0 2.1 8.8 4.9 Gross fair value of derivative contracts 8,035.9 8,511.0 4,321.2 4,201.0 Impact of netting and collateral (8,118.5 ) (8,317.6 ) (4,205.5 ) (3,879.2 ) Total fair value included in ‘Deposits with and receivables from broker-dealers, clearing organizations and counterparties’ $ (268.7 ) $ (46.4 ) Total fair value included in ‘Financial instruments owned, at fair value’ $ 186.1 $ 162.1 Total fair value included in ‘Payables to broker-dealers, clearing organizations and counterparties $ — $ 4.8 Fair value included in ‘Financial instruments sold, not yet purchased, at fair value’ $ 193.4 $ 317.0 (1) As of September 30, 2018 and 2017 , the Company’s derivative contract volume for open positions was approximately 10.6 million and 6.1 million contracts, respectively. The Company’s derivative contracts are principally held in its Commodities and Risk Management Services (“Commercial Hedging”) segment. The Company assists its Commercial Hedging segment clients in protecting the value of their future production by entering into option or forward agreements with them on an OTC basis. The Company also provides its Commercial Hedging segment clients with option products, including combinations of buying and selling puts and calls. The Company mitigates its risk by generally offsetting the client’s transaction simultaneously with one of the Company’s trading counterparties or will offset that transaction with a similar but not identical position on the exchange. The risk mitigation of these offsetting trades is not within the documented hedging designation requirements of the Derivatives and Hedging Topic of the ASC. These derivative contracts are traded along with cash transactions because of the integrated nature of the markets for these products. The Company manages the risks associated with derivatives on an aggregate basis along with the risks associated with its proprietary trading and market-making activities in cash instruments as part of its firm-wide risk management policies. In particular, the risks related to derivative positions may be partially offset by inventory, unrealized gains in inventory or cash collateral paid or received. The Company transacts in derivative instruments, which consist of futures, mortgage-backed TBA securities and forward settling transactions, that are used to manage risk exposures in the Company’s fixed income portfolio. The fair value of these transactions is recorded in deposits with and receivables from broker-dealers, clearing organizations, and counterparties. Realized and unrealized gains and losses on securities and derivative transactions are reflected in ‘trading gains, net’. The Company enters into TBA securities transactions for the sole purpose of managing risk associated with the purchase of mortgage pass-through securities. TBA securities are included within payables to broker-dealers, clearing organizations and counterparties. Forward settling securities represent non-regular way securities and are included in financial instruments owned and sold. As of September 30, 2018 , TBA and forward settling securities recorded within deposits with and receivables from broker-dealers, clearing organizations, and counterparties are summarized as follows (in millions): Gain / (Loss) Notional Amounts Unrealized gain on TBA securities purchased $ 1.2 $ 721.5 Unrealized loss on TBA securities purchased $ (0.6 ) $ 293.2 Unrealized gain on TBA securities sold $ 3.2 $ (1,099.5 ) Unrealized loss on TBA securities sold $ (1.5 ) $ (812.7 ) Unrealized loss on forward settling securities purchased $ 0.5 $ 614.3 Unrealized gain on forward settling securities sold $ 0.1 $ (427.2 ) The notional amounts of these instruments reflect the extent of the Company’s involvement in TBA and forward settling securities and do not represent counterparty exposure. The following table sets forth the Company’s net gains (losses) related to derivative financial instruments for the fiscal years ended September 30, 2018, 2017, and 2016 , in accordance with the Derivatives and Hedging Topic of the ASC. The net gains (losses) set forth below are included in ‘trading gains, net’ and ‘cost of sales of physical commodities’ in the consolidated income statements. Year Ended September 30, (in millions) 2018 2017 2016 Commodities $ 94.0 $ 47.3 $ 41.8 Foreign exchange 9.2 8.7 9.7 Interest rate and equity 1.0 (0.1 ) 0.8 TBA and forward settling securities 14.5 (2.5 ) (14.4 ) Net gains from derivative contracts $ 118.7 $ 53.4 $ 37.9 Credit Risk In the normal course of business, the Company purchases and sells financial instruments, commodities and foreign currencies as either principal or agent on behalf of its clients. If either the client or counterparty fails to perform, the Company may be required to discharge the obligations of the nonperforming party. In such circumstances, the Company may sustain a loss if the fair value of the financial instrument or foreign currency is different from the contract value of the transaction. The majority of the Company’s transactions and, consequently, the concentration of its credit exposure are with commodity exchanges, clients, broker-dealers and other financial institutions. These activities primarily involve collateralized and uncollateralized arrangements and may result in credit exposure in the event that a counterparty fails to meet its contractual obligations. The Company’s exposure to credit risk can be directly impacted by volatile financial markets, which may impair the ability of counterparties to satisfy their contractual obligations. The Company seeks to control its credit risk through a variety of reporting and control procedures, including establishing credit limits based upon a review of the counterparties’ financial condition and credit ratings. The Company monitors collateral levels on a daily basis for compliance with regulatory and internal guidelines and requests changes in collateral levels as appropriate. The Company is a party to financial instruments in the normal course of its business through client and proprietary trading accounts in exchange-traded and OTC derivative instruments. These instruments are primarily the execution of orders for commodity futures, options on futures and forward foreign currency contracts on behalf of its clients, substantially all of which are transacted on a margin basis. Such transactions may expose the Company to significant credit risk in the event margin requirements are not sufficient to fully cover losses which clients may incur. The Company controls the risks associated with these transactions by requiring clients to maintain margin deposits in compliance with individual exchange regulations and internal guidelines. The Company monitors required margin levels daily and, therefore, may require clients to deposit additional collateral or reduce positions when necessary. The Company also establishes credit limits for clients, which are monitored daily. The Company evaluates each client’s creditworthiness on a case by case basis. Clearing, financing, and settlement activities may require the Company to maintain funds with or pledge securities as collateral with other financial institutions. Generally, these exposures to both clients and counterparties are subject to master netting, or client agreements, which reduce the exposure to the Company by permitting receivables and payables with such clients to be offset in the event of a client default. Management believes that the margin deposits held as of September 30, 2018 and September 30, 2017 were adequate to minimize the risk of material loss that could be created by positions held at that time. Additionally, the Company monitors collateral fair value on a daily basis and adjusts collateral levels in the event of excess market exposure. Derivative financial instruments involve varying degrees of off-balance sheet market risk whereby changes in the fair values of underlying financial instruments may result in changes in the fair value of the financial instruments in excess of the amounts reflected in the consolidated balance sheets. Exposure to market risk is influenced by a number of factors, including the relationships between the financial instruments and the Company’s positions, as well as the volatility and liquidity in the markets in which the financial instruments are traded. The principal risk components of financial instruments include, among other things, interest rate volatility, the duration of the underlying instruments and changes in commodity pricing and foreign exchange rates. The Company attempts to manage its exposure to market risk through various techniques. Aggregate market limits have been established and market risk measures are routinely monitored against these limits.

Receivables from customers, net

Receivables from customers, net and notes receivable, net (Notes)	12 Months Ended
	Sep. 30, 2018
Receivables from customers and notes receivable, net [Abstract]
Receivables from Customers and Notes Receivable [Text Block]	Allowance for Doubtful Accounts Deposits with and receivables from broker-dealers, clearing organizations, and counterparties, net, receivables from clients, net, and notes receivable, net include an allowance for doubtful accounts, which reflects the Company’s best estimate of probable losses inherent in the accounts. The Company provides for an allowance for doubtful accounts based on a specific-identification basis. The Company continually reviews its allowance for doubtful accounts. The allowance for doubtful accounts related to deposits with and receivables from broker-dealers, clearing organizations, and counterparties was $48.0 million and $47.0 million as of September 30, 2018 and 2017 , respectively. The allowance for doubtful accounts related to receivables from clients was $10.2 million and $7.6 million as of September 30, 2018 and 2017 , respectively. The Company had no allowance for doubtful accounts related to notes receivable as of September 30, 2018 and 2017 . During the year ended September 30, 2018 , the Company recorded bad debt expense related to clients, net of recoveries, of $3.1 million , including provision net increases of $2.9 million , direct write-offs of $0.3 million , and recoveries of $0.1 million . The increase in bad debts during fiscal 2018 primarily related to $2.8 million of agricultural OTC client account deficits in the Commercial Hedging segment and $0.4 million of exchange-traded client account deficits in the Clearing & Execution Services segment, partially offset by a provision decrease in the Physical Commodities segment. During the year ended September 30, 2017, the Company recorded bad debt expense related to clients, net of recoveries, of $4.3 million , including provision increases of $4.2 million and direct write-offs of $0.1 million . The increase in bad debts during fiscal 2017 primarily related to $3.8 million of client deficits in the Commercial Hedging segment, primarily related to account deficits from South Korean and Dubai commercial LME clients, $0.2 million of uncollectible client receivables in the Physical Commodities segment, and $0.3 million of uncollectible client receivables in the Clearing & Execution Services segment, primarily related to our derivatives voice brokerage business. During first quarter of fiscal 2018 and the fourth quarter of fiscal 2017, the Company recorded charges to earnings of $1.0 million and $47.0 million , respectively, to record an allowance for doubtful accounts related to a bad debt incurred in the physical coal business conducted solely in INTL Asia Pte. Ltd., with a coal supplier (counterparty), as further discussed in Note 17 . During the year ended September 30, 2016, the Company recorded bad debt expense related to clients, net of recoveries, of $4.4 million , including provision increases of $4.2 million and direct write-offs of $0.4 million , offset by recoveries of $0.2 million . The increase in bad debts during fiscal 2016 primarily related to $3.6 million of client deficits in the Commercial Hedging segment, $0.4 million of uncollectible client receivables in the Physical Commodities segment, and $0.4 million of uncollectible service fees and notes in the Securities segment. Activity in the allowance for doubtful accounts for the years ended September 30, 2018, 2017, and 2016 was as follows: (in millions) 2018 2017 2016 Balance, beginning of year $ 54.6 $ 9.7 $ 11.2 Provision for bad debts 3.9 51.0 4.2 Charge-offs (0.3 ) (6.1 ) (5.7 ) Balance, end of year $ 58.2 $ 54.6 $ 9.7

Physical Commodities Inventory

Physical Commodities Inventory (Notes)	12 Months Ended
	Sep. 30, 2018
Physical Commodities Inventory [Abstract]
Inventory Disclosure [Text Block]	Physical Commodities Inventory The Company’s inventories consist of finished physical commodities. Inventories by component of the Company’s Physical Commodities segment are shown below. (in millions) September 30, September 30, Physical Ag & Energy (1) $ 114.7 $ 65.1 Precious metals - held by broker-dealer subsidiary (2) 42.1 13.3 Precious metals - held by non-broker-dealer subsidiaries (3) 65.7 46.4 Physical commodities inventory $ 222.5 $ 124.8 (1) Physical Ag & Energy maintains agricultural commodity inventories, including corn, soybeans, wheat, canola, coffee, cocoa, cotton, and others. The agricultural commodity inventories are carried at net realizable value, which approximates fair value less disposal costs, with changes in net realizable value included as a component of ‘cost of sales of physical commodities’ on the consolidated income statement. The agricultural inventories have reliable, readily determinable and realizable market prices, have relatively insignificant costs of disposal and are available for immediate delivery. Physical Ag & Energy also maintains energy inventory, primarily propane, gasoline, and kerosene, which are valued at the lower of cost or net realizable value. (2) Precious metals held by the Company’s subsidiary, INTL FCStone Ltd, a United Kingdom based broker-dealer subsidiary, is measured at net realizable value, with changes in net realizable value included as a component of ‘trading gains, net’ on the consolidated income statement, in accordance with U.S. GAAP accounting requirements for broker-dealers. (3) Precious metals inventory held by subsidiaries that are not broker-dealers are valued at the lower of cost or net realizable value. The Company has recorded lower of cost or net realizable value adjustments for certain precious metals inventory of $0.4 million and $0.7 million as of September 30, 2018 and 2017 , respectively. The adjustments are included in ‘cost of sales of physical commodities’ in the consolidated income statements.

Property and Equipment, net (No

Property and Equipment, net (Notes)	12 Months Ended
	Sep. 30, 2018
Property and Equipment, net [Abstract]
Property, Plant and Equipment Disclosure [Text Block]	Property and Equipment, net Property and equipment are stated at cost, and reported net of accumulated depreciation on the consolidated balance sheets. Depreciation on property and equipment is calculated using the straight-line method over the estimated useful lives of the assets. The estimated useful lives of property and equipment range from 3 to 10 years. During the fiscal years ended September 30, 2018, 2017, and 2016 , depreciation expense was $9.4 million , $7.0 million and $6.6 million , respectively. A summary of property and equipment, at cost less accumulated depreciation as of September 30, 2018 and 2017 is as follows: (in millions) September 30, 2018 September 30, 2017 Property and equipment: Furniture and fixtures $ 8.7 $ 7.2 Software 30.5 25.3 Equipment 24.7 22.6 Leasehold improvements 17.0 15.4 Total property and equipment 80.9 70.5 Less accumulated depreciation (38.5 ) (31.8 ) Property and equipment, net $ 42.4 $ 38.7

Goodwill (Notes)

Goodwill (Notes)	12 Months Ended
	Sep. 30, 2018
Goodwill [Abstract]
Goodwill Disclosure [Text Block]	Goodwill Goodwill allocated to the Company’s operating segments as of September 30, 2018 and 2017 is as follows: (in millions) September 30, September 30, Commercial Hedging $ 30.3 $ 30.7 Global Payments 8.9 6.3 Physical Commodities 2.4 2.4 Securities 6.8 7.7 Goodwill $ 48.4 $ 47.1 The Company recorded $1.3 million and zero in foreign exchange translation losses on goodwill within the Commercial Hedging and Securities operating segments for the years ended September 30, 2018 and 2017, respectively. The Company also recorded additional goodwill of $2.6 million within the Global Payments operating segment related to the acquisition of PayCommerce Financial Solutions, LLC as discussed further in Note 19 .

Intangible Assets (Notes)

Intangible Assets (Notes)	12 Months Ended
	Sep. 30, 2018
Intangible Assets [Abstract]
Intangible Assets Disclosure [Text Block]	Intangible Assets During the year ended September 30, 2018, the Company recorded additional client base intangible assets of $1.4 million as part of the PayCommerce Financial Solutions, LLC acquisition. See Note 19 - Acquisitions for additional discussion. The gross and net carrying values of intangible assets as of the balance sheet dates, by major intangible asset class are as follows (in millions): September 30, 2018 September 30, 2017 Gross Amount Accumulated Amortization Net Amount Gross Amount Accumulated Amortization Net Amount Intangible assets subject to amortization: Trade name $ — $ — $ — $ — $ — $ — Software programs/platforms 2.7 (2.6 ) 0.1 2.7 (2.5 ) 0.2 Client base 21.4 (10.1 ) 11.3 20.0 (7.9 ) 12.1 Total intangible assets $ 24.1 $ (12.7 ) $ 11.4 $ 22.7 $ (10.4 ) $ 12.3 Amortization expense related to intangible assets was $2.3 million , $2.8 million , and $1.6 million for the fiscal years ended September 30, 2018, 2017, and 2016 , respectively. The estimated future amortization expense as of September 30, 2018 is as follows (in millions): Year ending September 30, 2019 $ 2.5 2020 2.2 2021 2.2 2022 1.0 2023 and thereafter 3.5 $ 11.4

Credit Facilities (Notes)

Credit Facilities (Notes)	12 Months Ended
	Sep. 30, 2018
Credit Facilities [Abstract]
Debt Disclosure [Text Block]	Credit Facilities Variable-Rate Credit Facilities The Company has four committed credit facilities under which the Company and its subsidiaries may borrow up to $594.5 million , subject to the terms and conditions for these facilities. The amounts outstanding under these credit facilities are short term borrowings and carry variable rates of interest, thus approximating fair value. The Company’s credit facilities are as follows: • A three-year first-lien senior secured committed syndicated loan facility under which $262.0 million is available to the Company for general working capital requirements and capital expenditures. The credit facility is secured by a first priority lien on substantially all of the assets of the Company and those of our subsidiaries that guarantee the credit facility. Unused portions of the loan facility require a commitment fee of 0.625% on the unused commitment. Borrowings under the facility bear interest at the Eurodollar Rate, as defined, plus 3.00% or the Base Rate, as defined, plus 2.00% , and averaged 5.17% as of September 30, 2018. The agreement contains financial covenants related to consolidated tangible net worth, consolidated funded debt to net worth ratio, consolidated fixed charge coverage ratio and consolidated net unencumbered liquid assets, as defined. The agreement also contains a non-financial covenant related to the allowable annual consolidated capital expenditures permitted under the agreement. The Company was in compliance with all covenants under the loan facility as of September 30, 2018 . • An unsecured syndicated committed line of credit under which $75.0 million is available to the Company’s wholly owned subsidiary, INTL FCStone Financial to provide short term funding of margin to commodity exchanges as necessary. This line of credit is subject to annual review, and the continued availability of this line of credit is subject to INTL FCStone Financial’s financial condition and operating results continuing to be satisfactory as set forth in the agreement. Unused portions of the margin line require a commitment fee of 0.50% on the unused commitment. Borrowings under the margin line are on a demand basis and bear interest at the Base Rate, as defined, plus 2.00% , which was 7.25% as of September 30, 2018 . The agreement contains financial covenants related to INTL FCStone Financial’s tangible net worth, excess net capital and maximum net loss over a trailing twelve month period, as defined. INTL FCStone Financial was in compliance with these covenants as of September 30, 2018 . The facility is guaranteed by the Company. • A syndicated committed borrowing facility under which $232.5 million is available to the Company’s wholly owned subsidiary, FCStone Merchant Services, LLC (“FCStone Merchants”) for financing traditional commodity financing arrangements and commodity repurchase agreements. The facility is secured by the assets of FCStone Merchants, and guaranteed by the Company. Unused portions of the borrowing facility require a commitment fee of 0.38% on the unused commitment. The borrowings outstanding under the facility bear interest at a rate per annum equal to the Eurodollar Rate plus Applicable Margin, as defined, or the Base Rate plus Applicable Margin, as defined, which averaged 4.77% as of September 30, 2018 . The agreement contains financial covenants related to tangible net worth, as defined. FCStone Merchants was in compliance with this covenant as of September 30, 2018 . • An unsecured syndicated committed borrowing facility under which $25.0 million is available to the Company’s wholly owned subsidiary, INTL FCStone Ltd for short term funding of margin to commodity exchanges. The borrowings outstanding under the facility bear interest at a rate per annum equal to 2.50% plus the Federal Funds Rate, as defined. The agreement contains financial covenants related to consolidated tangible net worth, as defined. INTL FCStone Ltd was in compliance with this covenant as of September 30, 2018 . The facility is guaranteed by the Company. The Company also has a secured, uncommitted loan facility, under which INTL FCStone Ltd may borrow up to £20.0 million , collateralized by commodities warehouse receipts, to facilitate financing of commodities under repurchase agreement services to its clients, subject to certain terms and conditions of the credit agreement. The Company also has a secured, uncommitted loan facility, under which INTL FCStone Financial may borrow up to $75.0 million , collateralized by commodities warehouse receipts, to facilitate U.S. commodity exchange deliveries of its clients, subject to certain terms and conditions of the credit agreement. There were $0 and $23.0 million in borrowings outstanding under this credit facility at September 30, 2018 and 2017, respectively. Borrowings under this facility bear interest at the Fed Funds Rate, as defined, plus 2.5% . The Company also has a secured uncommitted loan facility under which INTL FCStone Financial may borrow for short term funding of firm and client securities margin requirements, subject to certain terms and conditions of the agreement. The uncommitted amount available to be borrowed is not specified, and all requests for borrowing are subject to the sole discretion of the lender. The facility bears interest at a rate per annum equal to such rate in respect of such day as determined by the bank in its sole discretion. In the event that the Company fails to pay the principal and interest on the scheduled due date, the facilities bear penalty interest at a rate equal to the Federal Funds rate plus 2% . The amounts borrowed under the facilities are payable on demand. At September 30, 2018 and 2017, the Company had $14.0 million and $0 , respectively, of borrowings outstanding under this credit facility. The interest rate associated with the borrowings outstanding as of September 30, 2018, was 2.88% . The Company also has secured uncommitted loan facilities under which INTL FCStone Financial may borrow up to $150.0 million for short term funding of firm and client securities margin requirements, subject to certain terms and conditions of the agreements. The loans are payable on demand and bear interest at a rate mutually agreed to with the lender. The borrowings are secured by first liens on firm owned marketable securities or client owned securities which have been pledged to the Company. There were $0 and $11.0 million in borrowings outstanding under these credit facilities at September 30, 2018 and 2017, respectively. In August 2018, the Company executed a secured uncommitted loan facility under which FCStone Merchants could borrow up to $15.0 million to facilitate the financing of inventory of commodities and other products or goods approved by the lender in its sole discretion, subject to certain terms and conditions of the loan facility agreement. The loan facility is collateralized by a first priority security interest in goods and inventory of FCStone Merchants that is (a) either located outside of the U.S. and Canada or in transit to a destination outside the U.S. or Canada and (b) acquired with any extension of credit (whether in the form of a loan or by the issuance of a letter of credit) under the loan facility. Loans under the facility accrue interest at a per annum rate equal to the applicable Cost of Funds Rate, as defined, plus 3.00% or at the Base Rate, as defined, plus 2.00% . Letters of credit under the facility accrue a fee at the per annum rate of 2.75% . There were $3.8 million in borrowings outstanding under this credit facility at September 30, 2018. The interest rate associated with these borrowings was approximately 5.4% . In December 2018, the Company executed an amendment to increase the availability under this uncommitted loan facility to $20.0 million . Note Payable to Bank In April 2015, the Company obtained a $4.0 million loan from a commercial bank, secured by equipment purchased with the proceeds. The note is payable in monthly installments, ending in March 2020. The note bears interest at a rate per annum equal to LIBOR plus 2.00% . Senior Unsecured Notes In July 2013, the Company completed an offering of $45.5 million aggregate principal amount of the Company’s 8.5% Senior Notes due 2020 (the “Notes”). The net proceeds of the sale of the Notes were being used for general corporate purposes. The Notes bore interest at a rate of 8.5% per year (payable quarterly on January 30, April 30, July 30 and October 30 of each year). The Notes were scheduled to mature on July 30, 2020. The Company could redeem the Notes, in whole or in part, at any time on and after July 30, 2016, at a redemption price equal to 100% of the principal amount redeemed plus accrued and unpaid interest to, but not including, the redemption date. The Company incurred debt issuance costs of $1.7 million in connection with the issuance of the Notes, which were being amortized over the term of the Notes. On September 15, 2016, the Company provided notice, through the trustee of the Notes, to the record holders of the Notes that the Company would redeem the outstanding $45.5 million aggregate principal amount of the Notes in full. On October 15, 2016, the Company redeemed the Notes at a prices equal to 100% of the principal amount redeemed plus accrued and unpaid interest to, but not including, October 15, 2016. The remaining unamortized deferred financing costs of $1.0 million were written off in connection with the redemption of the Notes and are included in ‘interest expense’ in the consolidated income statement for the year ended September 30, 2017. The following table sets forth a listing of credit facilities, the current committed amounts, as of the report date, on the facilities, and outstanding borrowings on the facilities as well as indebtedness on a promissory note as of September 30, 2018 and 2017 : (in millions) Credit Facilities Amounts Outstanding Borrower Security Renewal / Expiration Date Total Commitment September 30, September 30, Committed Credit Facilities INTL FCStone Inc. Pledged shares of certain subsidiaries March 18, 2019 $ 262.0 $ 208.2 $ 150.0 INTL FCStone Financial Inc. None April 4, 2019 75.0 — — FCStone Merchants Services, LLC Certain commodities assets November 1, 2019 232.5 128.0 44.2 INTL FCStone Ltd. None January 31, 2019 25.0 — — $ 594.5 336.2 194.2 Uncommitted Credit Facilities INTL FCStone Financial Inc. Commodities warehouse receipts and certain pledged securities n/a — 14.0 34.0 INTL FCStone Ltd. Commodities warehouse receipts n/a — — — FCStone Merchants Services, LLC Certain commodities assets n/a — 3.8 — Note Payable to Bank Monthly installments, due March 2020 and secured by certain equipment 1.2 2.0 Total Payables to lenders under loans $ 355.2 $ 230.2 As reflected above, $362 million of the Company’s committed credit facilities are scheduled to expire during the fiscal year ended September 30, 2019. The Company intends to renew or replace these facilities as they expire, and based on the Company’s liquidity position and capital structure, the Company believes it will be able to do so.

Commitments and Contingencies (

Commitments and Contingencies (Notes)	12 Months Ended
	Sep. 30, 2018
Commitments and Contingencies [Abstract]
Commitments and Contingencies Disclosure [Text Block]	Commitments and Contingencies Legal and Regulatory Proceedings Certain conditions may exist as of the date the financial statements are issued, which may result in a loss to the Company but which will only be resolved when one or more future events occur or fail to occur. The Company assesses such contingent liabilities, and such assessment inherently involves an exercise of judgment. In assessing loss contingencies related to legal and regulatory proceedings that are pending against the Company or unasserted claims that may result in such proceedings, the Company’s legal counsel evaluates the perceived merits of any legal or regulatory proceedings or unasserted claims as well as the perceived merits of the amount of relief sought or expected to be sought therein. If the assessment of a contingency indicates that it is probable that a material loss had been incurred at the date of the financial statements and the amount of the liability can be estimated, then the estimated liability would be accrued in the Company’s financial statements. If the assessment indicates that a potentially material loss contingency is not probable, but is reasonably possible, or is probable but cannot be estimated, then the nature of the contingent liability, together with an estimate of the range of possible loss if determinable and material, would be disclosed. Neither accrual nor disclosure is required for loss contingencies that are deemed remote. The Company accrues legal fees related to contingent liabilities as they are incurred. From time to time and in the ordinary course of business, the Company is involved in various legal actions and proceedings, including tort claims, contractual disputes, employment matters, workers’ compensation claims and collections. The Company carries insurance that provides protection against certain types of claims, up to the limits of the respective policy. Additionally, the Company is subject to extensive regulation and supervision by U.S. federal and international governmental agencies and various self-regulatory organizations. The Company and its advisors periodically engage with such regulatory agencies and organizations, in the context of examinations or otherwise, to respond to inquiries, informational requests, and investigations. From time to time, such engagements result in regulatory complaints or other matters, the resolution of which can include fines and other remediation. As of September 30, 2018 and 2017 , the consolidated balance sheets include loss contingency accruals, recorded during and prior to these fiscal years then ended, which are not material, individually or in the aggregate, to the Company’s financial position or liquidity. In the opinion of management, possible exposure from loss contingencies in excess of the amounts accrued, and in addition to the possible losses discussed below, is not material to the Company’s earnings, financial position or liquidity. The following is a summary of a significant legal matter involving the Company: Sentinel Litigation Prior to the July 1, 2015 merger into INTL FCStone Financial, our subsidiary, FCStone, LLC, had a portion of its excess segregated funds invested with Sentinel Management Group Inc. (“Sentinel”), a registered futures commission merchant (“FCM”) and an Illinois-based money manager that provided cash management services to other FCMs. In August 2007, Sentinel halted redemptions to clients and sold certain of the assets it managed to an unaffiliated third party at a significant discount. On August 17, 2007, subsequent to Sentinel’s sale of certain assets, Sentinel filed for bankruptcy protection. In aggregate, $15.5 million of FCStone, LLC’s $21.9 million in invested funds were returned to it before and after Sentinel’s bankruptcy petition. A further $2.0 million was held by the bankruptcy trustee in reserve in the name of FCStone, LLC. In August 2008, the bankruptcy trustee of Sentinel filed adversary proceedings against FCStone, LLC, and a number of other FCMs, seeking recovery of pre- and post-petition transfers totaling $15.5 million . On April 23, 2018, following ten years of legal proceedings and a final ruling by the United States Court of Appeals for the Seventh Circuit against the trustee in favor of INTL FCStone Financial, the United States Supreme Court denied the trustee’s petition for writ of certiorari. Following this, on May 1, 2018, INTL FCStone Financial received funds from the reserve account in the amount of $2.0 million . This amount is presented in ‘Other gains’ in the consolidated income statement for the year ended September 30, 2018. Our assessments are based on estimates and assumptions that have been deemed reasonable by management, but that may later prove to be incomplete or inaccurate, and unanticipated events and circumstances may occur that might cause us to change those estimates and assumptions. Contractual Commitments Operating Leases The Company is obligated under various noncancelable operating leases for the rental of office facilities, automobiles, service obligations and certain office equipment, and accounts for these lease obligations on a straight line basis. The expense associated with operating leases was $12.0 million , $11.3 million and $9.9 million , for fiscal years ended September 30, 2018, 2017, and 2016 , respectively. The expenses associated with the operating leases and service obligations are reported in the consolidated income statements in ‘occupancy and equipment rental’, ‘transaction-based clearing expenses’ and ‘other’ expenses. Future aggregate minimum lease payments under noncancelable operating leases as of September 30, 2018 are as follows: (in millions) Year ending September 30, 2019 $ 10.1 2020 9.3 2021 8.1 2022 5.8 2023 4.5 Thereafter 5.6 $ 43.4 Purchase Commitments The Company determines an estimate of contractual purchase commitments in the ordinary course of business primarily for the purchase of precious metals and agricultural and energy commodities. Unpriced contract commitments have been estimated using September 30, 2018 fair values. The purchase commitments and other obligations as of September 30, 2018 for less than one year, one to three years and three to five years were $1,204.7 million , $1.7 million and $1.8 million , respectively. There were $2.0 million in purchase commitments and other obligations after five years as of September 30, 2018 . The purchase commitments for less than one year will be offset by corresponding sales commitments of $1,406 million . Exchange Member Guarantees The Company is a member of various exchanges that trade and clear futures and option contracts. In connection with the Sterne acquisition, the Company is also a member of and provides guarantees to securities clearinghouses and exchanges in connection with client trading activities. Associated with its memberships, the Company may be required to pay a proportionate share of the financial obligations of another member who may default on its obligations to the exchanges. While the rules governing different exchange memberships vary, in general the Company’s guarantee obligations would arise only if the exchange had previously exhausted its resources. In addition, any such guarantee obligation would be apportioned among the other non-defaulting members of the exchange. Any potential contingent liability under these arrangements is not quantifiable and could exceed the cash and securities it has posted to the clearinghouse as collateral. The Company has not recorded any contingent liability in the consolidated financial statements for these agreements and believes that any potential requirement to make payments under these agreements is remote. Self-Insurance The Company self-insures its costs related to medical and dental claims. The Company is self-insured, up to a stop loss amount, for eligible participating employees and retirees, and for qualified dependent medical and dental claims, subject to deductibles and limitations. Liabilities are recognized based on claims filed and an estimate of claims incurred but not reported. The Company has purchased stop-loss coverage to limit its exposure on a per claim basis and in aggregate in the event that aggregated actual claims would exceed 120% of actuarially estimated claims. The Company is insured for covered costs in excess of these limits. Although the ultimate outcome of these matters may exceed the amounts recorded and additional losses may be incurred, the Company does not believe that any additional potential exposure for such liabilities will have a material adverse effect on the Company’s consolidated financial position or results of operations. As of September 30, 2018 and 2017 , the Company had $0.8 million accrued for self-insured medical and dental claims included in ‘accounts payable and other liabilities’ in the consolidated balance sheets.

Regulatory Requirements and Sub

Regulatory Requirements and Subsidiary Dividend Restrictions (Notes)	12 Months Ended
	Sep. 30, 2018
Capital and Other Regulatory Requirements [Abstract]
Regulatory Capital Requirements under Banking Regulations [Text Block]	Regulatory Requirements and Subsidiary Dividend Restrictions The Company’s subsidiary INTL FCStone Financial is registered as a broker dealer and member of the Financial Industry Regulatory Authority (“FINRA”) subject to the SEC Uniform Net Capital Rule 15c3-1, which requires the maintenance of minimum net capital. INTL FCStone Financial is also a commodity futures commission merchant registered with the CFTC and subject to the net capital requirements of the CFTC Regulation 1.17. Under the more restrictive of these rules, INTL FCStone Financial is required to maintain “adjusted net capital”, equivalent to the greater of $1,000,000 or 8 percent of client and nonclient risk maintenance margin requirements on all positions, as defined in such rules, regulations, and requirements. Net capital and the related net capital requirement may fluctuate on a daily basis. INTL FCStone Financial also has restriction on dividends, which restricts the withdrawal of equity capital if the planned withdrawal would reduce net capital, subsequent to haircuts and charges, to an amount less than 120% of the greatest minimum requirement. INTL FCStone Financial as a registered securities carrying broker dealer is also subject to Rule 15c3-3 of the Securities Exchange Act of 1934 (“Rule 15c3-3”), which requires the Company to maintain separate accounts for the benefit of securities clients and proprietary accounts of broker dealers (“PABs”). These client protection rules require the Company to maintain special reserve bank accounts (“SRBAs”) for the exclusive benefit of securities clients and PABs. Pursuant to the requirements of the Commodity Exchange Act, funds deposited by clients of INTL FCStone Financial relating to their trading of futures and options on futures on a U.S. commodities exchange must be carried in separate accounts which are designated as segregated clients’ accounts. Pursuant to the requirements of the CFTC, funds deposited by clients of INTL FCStone Financial relating to their trading of futures and options on futures traded on, or subject to the rules of, a foreign board of trade must be carried in separate accounts in an amount sufficient to satisfy all of INTL FCStone Financial’s current obligations to clients trading foreign futures and foreign options on foreign commodity exchanges or boards of trade, which are designated as secured clients’ accounts. See below for additional information regarding INTL FCStone Financial’s calculation of segregated and secured client funds. The Company’s subsidiary SA Stone Wealth Management Inc. (formerly Sterne Agee Financial Services, Inc.) is subject to the SEC Uniform Net Capital Rule 15c3-1 under the Securities Exchange Act of 1934. The Company’s subsidiary INTL FCStone Ltd is regulated by the Financial Conduct Authority (“FCA”), the regulator of the financial services industry in the United Kingdom, as a Financial Services Firm under part IV of the Financial Services and Markets Act 2000. The regulations impose regulatory capital, as well as conduct of business, governance, and other requirements. The conduct of business rules include those that govern the treatment of client money and other assets which under certain circumstances for certain classes of client must be segregated from the firm’s own assets. The Company’s subsidiary INTL FCStone Pty Ltd is regulated by the Australian Securities and Investment Commission and is subject to a net tangible asset capital requirement. INTL FCStone DTVM Ltda. (“INTL FCStone DTVM”) is a registered broker-dealer and regulated by the Brazilian Central Bank and Securities and Exchange Commission of Brazil, and is subject to a capital adequacy requirement. INTL Gainvest S.A. and INTL CIBSA S.A. are regulated by the Comision Nacional de Valores, and are subject to net capital and capital adequacy requirements. All subsidiaries of the Company are in compliance with all of their regulatory requirements as of September 30, 2018 , as follows: (in millions) As of September 30, 2018 Subsidiary Regulatory Authority Requirement Type Actual Minimum Requirement INTL FCStone Financial Inc. SEC and CFTC Net capital $ 167.7 $ 101.4 INTL FCStone Financial Inc. CFTC Segregated funds $ 2,637.0 $ 2,579.7 INTL FCStone Financial Inc. CFTC Secured funds $ 148.9 $ 132.8 INTL FCStone Financial Inc. SEC Customer reserve * $ 6.4 INTL FCStone Financial Inc. SEC PAB reserve $ 0.3 $ — SA Stone Wealth Management Inc. SEC Net capital $ 4.6 $ 0.4 INTL FCStone Ltd FCA (United Kingdom) Net capital $ 193.1 $ 95.9 INTL FCStone Ltd FCA (United Kingdom) Segregated funds $ 187.3 $ 182.1 INTL Netherlands BV FCA (United Kingdom) Net capital $ 193.0 $ 95.9 INTL FCStone DTVM Ltda. Brazilian Central Bank and Securities and Exchange Commission of Brazil Capital adequacy $ 11.2 $ 2.1 INTL Gainvest S.A. National Securities Commission ("CNV") Capital adequacy $ 4.2 $ 0.1 INTL Gainvest S.A. CNV Net capital $ 1.2 $ 0.1 INTL CIBSA S.A. CNV Capital adequacy $ 4.4 $ 0.5 INTL CIBSA S.A. CNV Net capital $ 3.1 $ 0.3 * As of September 30, 2018, the Company had no balance in the customer reserve SRBA. As a result of the reserve requirement determined through the weekly computation, the Company made a deposit to the customer reserve SRBA of $11.4 million on October 2, 2018, to meet the customer segregation requirements under Rule 15c3-3. Certain other non-U.S. subsidiaries of the Company are also subject to capital adequacy requirements promulgated by authorities of the countries in which they operate. As of September 30, 2018 , these subsidiaries were in compliance with their local capital adequacy requirements.

Commodity and Other Repurchase

Commodity and Other Repurchase Agreements (Notes)	12 Months Ended
	Sep. 30, 2018
Commodity and Other Repurchase Agreements [Abstract]
Repurchase Agreements, Resale Agreements, Securities Borrowed, and Securities Loaned Disclosure [Text Block]	Securities and Commodity Financing Transactions The Company’s outstanding notes receivable in connection with repurchase agreements for agricultural and energy commodities, whereby the clients sell to the Company certain commodity inventory and agree to repurchase the commodity inventory at a future date at a fixed price were $1.9 million and $0.8 million as of September 30, 2018 and 2017, respectively. 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 as collateralized financings at their contractual amounts plus accrued interest. The related interest is recorded in the 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 September 30, 2018 and 2017, financial instruments owned, at fair value of $123.0 million and $19.4 million , respectively, 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 consolidated balance sheet. In addition, as of September 30, 2018 and 2017, the Company pledged financial instruments owned, at fair value of $1,481.1 million and $1,306.4 million , respectively, and securities received under reverse repurchase agreements of $369.8 million and $100.2 million , respectively, to cover collateral requirements for tri-party repurchase agreements. For these securities, the counterparties do not have the right to sell or repledge the collateral and, therefore, they have not been parenthetically disclosed on the consolidated balance sheet. The Company also has repledged securities borrowed and client securities held under custodial clearing arrangements to collateralize securities loaned agreements with a fair value of $267.9 million and $108.4 million as of September 30, 2018 and 2017, respectively. Additionally, the Company has also pledged financial instruments owned of $27.1 million and $12.7 million as of September 30, 2018 and 2017, respectively, to collateralize uncommitted loan facilities with certain banks as discussed further in Note 10 . At September 30, 2018 and 2017, the Company had 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 September 30, 2018 and 2017 was $1,294.8 million and $631.7 million , respectively, of which $473.9 million and $306.9 million , respectively, was used to cover securities sold short which are recorded in financial instruments sold, not yet purchased on the 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. The following tables provide the contractual maturities of gross obligations under repurchase and securities lending agreements as of September 30, 2018 and 2017 (in millions): September 30, 2018 Overnight and Open Less than 30 Days 30-90 Days Total Securities sold under agreements to repurchase $ 934.9 $ 661.3 $ 340.5 $ 1,936.7 Securities loaned 277.9 — — 277.9 Gross amount of secured financing $ 1,212.8 $ 661.3 $ 340.5 $ 2,214.6 September 30, 2017 Overnight and Open Less than 30 Days 30-90 Days Total Securities sold under agreements to repurchase $ 640.2 $ 432.9 $ 320.0 $ 1,393.1 Securities loaned 111.1 — — 111.1 Gross amount of secured financing $ 751.3 $ 432.9 $ 320.0 $ 1,504.2 The following table provides the underlying collateral types of the gross obligations under repurchase and securities lending agreements as of September 30, 2018 and 2017 (in millions): Securities sold under agreements to repurchase: September 30, 2018 September 30, 2017 U.S. Treasury obligations $ 39.6 $ 7.0 U.S. government agency obligations 461.7 332.6 Asset-backed obligations 50.0 36.4 Agency mortgage-backed obligations 1,385.4 1,017.1 Total securities sold under agreements to repurchase $ 1,936.7 $ 1,393.1 Securities loaned: Equity securities 277.9 111.1 Total securities loaned 277.9 111.1 Gross amount of secured financing $ 2,214.6 $ 1,504.2

Share-Based Compensation (Notes

Share-Based Compensation (Notes)	12 Months Ended
	Sep. 30, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Disclosure of Compensation Related Costs, Share-based Payments [Text Block]	Share-Based Compensation Share-based compensation expense is included in ‘compensation and benefits’ in the consolidated income statements and totaled $6.6 million , $6.3 million and $5.1 million for the fiscal years ended September 30, 2018, 2017, and 2016 , respectively. Stock Option Plans The Company sponsors a stock option plan for its directors, officers, employees and consultants. The 2013 Stock Option Plan, which was approved by the Company’s Board of Directors and shareholders, authorizes the Company to issue stock options covering up to 1.0 million shares of the Company’s common stock. As of September 30, 2018 , there were 0.6 million shares authorized for future grant under this plan. Awards that expire or are canceled generally become available for issuance again under the plan. The Company settles stock option exercises with newly issued shares of common stock. Fair value is estimated at the grant date based on a Black-Scholes-Merton option-pricing model using the following weighted-average assumptions: Year Ended September 30, 2018 2017 2016 Expected stock price volatility 30 % 31 % 28 % Expected dividend yield — % — % — % Risk free interest rate 1.23 % 0.99 % 0.83 % Average expected life (in years) 3.06 3.08 3.06 Expected stock price volatility rates are primarily based on the historical volatility. The Company has not paid dividends in the past and does not currently expect to do so in the future. Risk free interest rates are based on the U.S. Treasury yield curve in effect at the time of grant for periods corresponding with the expected life of the option or award. The average expected life represents the estimated period of time that options or awards granted are expected to be outstanding, based on the Company’s historical share option exercise experience for similar option grants. The weighted average fair value of options issued during fiscal years ended September 30, 2018, 2017, and 2016 was $9.79 , $8.67 and $6.40 , respectively. The following is a summary of stock option activity for the year ended September 30, 2018 : Shares Available for Grant Number of Options Outstanding Weighted Average Exercise Price Weighted Average Grant Date Fair Value Weighted Average Remaining Term (in years) Aggregate Intrinsic Value ($ millions) Balances at September 30, 2017 652,494 881,403 $ 27.31 $ 11.55 3.57 $ 9.8 Granted (79,800 ) 79,800 $ 44.17 $ 9.79 Exercised (110,423 ) $ 23.79 $ 7.98 Forfeited 13,324 (13,324 ) $ 33.19 $ 7.14 Expired 2,002 (2,002 ) $ 32.60 $ 6.78 Balances at September 30, 2018 588,020 835,454 $ 29.27 $ 11.93 3.01 $ 15.9 Exercisable at September 30, 2018 314,366 $ 27.16 $ 11.68 2.81 $ 6.7 The total compensation cost not yet recognized for non-vested awards of $3.0 million as of September 30, 2018 has a weighted-average period of 3.13 years over which the compensation expense is expected to be recognized. The total intrinsic value of options exercised during fiscal years 2018, 2017 and 2016 was $2.1 million , $2.6 million and $1.9 million , respectively. The options outstanding as of September 30, 2018 broken down by exercise price are as follows: Exercise Price Number of Options Outstanding Weighted Average Exercise Price Weighted Average Remaining Term $ — - $ 5.00 — n/a n/a $ 5.00 - $ 10.00 — n/a n/a $ 10.00 - $ 15.00 — n/a n/a $ 15.00 - $ 20.00 — n/a n/a $ 20.00 - $ 25.00 28,668 $ 20.54 0.27 $ 25.00 - $ 30.00 580,000 $ 25.91 3.37 $ 30.00 - $ 35.00 49,656 $ 31.37 1.28 $ 35.00 - $ 40.00 100,330 $ 38.77 2.27 $ 40.00 - $ 45.00 74,800 $ 43.88 3.30 $ 45.00 - $ 50.00 — n/a n/a $ 50.00 - $ 55.00 2,000 $ 55.28 3.89 835,454 $ 29.27 3.01 Restricted Stock Plan The Company sponsors a restricted stock plan for its directors, officers and employees. The Company’s 2017 restricted stock plan, which was approved by the Company’s Board of Directors and shareholders, authorizes up to 1.5 million shares to be issued. As of September 30, 2018 , 1.4 million shares were authorized for future grant under the restricted stock plan. Awards that expire or are canceled generally become available for issuance again under the plan. The Company utilizes newly issued shares of common stock to make restricted stock grants. The following is a summary of restricted stock activity through September 30, 2018 : Shares Available for Grant Number of Shares Outstanding Weighted Average Grant Date Fair Value Weighted Average Remaining Term (in years) Aggregate Intrinsic Value ($ millions) Balances at September 30, 2017 1,459,976 354,474 $ 33.34 1.26 $ 13.6 Granted (85,404 ) 85,404 $ 44.86 Vested (162,544 ) $ 31.14 Forfeited 2,706 (2,706 ) $ 36.24 Balances at September 30, 2018 1,377,278 274,628 $ 38.20 1.15 $ 13.3 The total compensation cost not yet recognized of $6.8 million as of September 30, 2018 has a weighted-average period of 1.15 years over which the compensation expense is expected to be recognized. Compensation expense is amortized on a straight-line basis over the vesting period. Restricted stock grants are included in the Company’s total issued and outstanding common shares.

Retirement Plans (Notes)

Retirement Plans (Notes)	12 Months Ended
	Sep. 30, 2018
Retirement Benefits [Abstract]
Pension and Other Postretirement Benefits Disclosure [Text Block]	Note 15 – Retirement Plans Defined Benefit Retirement Plans The Company has a frozen qualified defined benefit pension plan (the “Qualified Plan”) and a nonqualified defined benefit pension plan (the “Nonqualified Plan”), and recognizes their funded status, measured as the difference between the fair value of the plan assets and the projected benefit obligation, in “other assets” or “accounts payable and other accrued liabilities” in the consolidated balance sheets, depending on the funded status of each plan. The Qualified Plan assets, which are managed in a third-party trust, primarily consist of a diversified blend of approximately 80% debt securities and 20% equity investments and had a total fair value of $35.6 million and $36.3 million as of September 30, 2018 and 2017, respectively. All Qualified Plan assets fall within Level 2 of the fair value hierarchy. The benefit obligation associated with the Qualified Plan will vary over time only as a result of changes in market interest rates, the life expectancy of the plan participants, and benefit payments, since the accrual of benefits was suspended when the Qualified Plan was frozen in 2006. The benefit obligation was $32.5 million and $34.7 million and the discount rate assumption used in the measurement of this obligation was 4.20% and 3.75% as of September 30, 2018 and 2017, respectively. Related to the Qualified Plan, the Company’s net liability for retirement costs had a funded status of $3.1 million and $1.6 million as of September 30, 2018 and 2017, respectively. The Nonqualified Plan assets had a total fair value of less than $0.1 million as of September 30, 2018 and 2017. The benefit obligation associated with the Nonqualified Plan will vary over time only as a result of changes in market interest rates, the life expectancy of the plan participants, and benefit payments. There are no active participants in the Nonqualified plan. The benefit obligation was $1.6 million and $1.8 million as of September 30, 2018 and 2017, respectively. Related to the Nonqualified Plan, the Company’s unfunded pension obligation was $1.6 million and $1.7 million as of September 30, 2018 and 2017, respectively. The Company recognized a net periodic benefit $0.2 million and $0.3 million for the year ended September 30, 2018 and 2017, respectively. The net periodic benefit cost associated with the plans was $0.2 million for the year ended September 30, 2016. The expected long-term return on plan assets assumption is 4.50% for 2018. The Company made contributions of $1.0 million and $2.0 million to the plans in the years ended September 30, 2018 and 2017, respectively. The Company complies with minimum funding requirements. The estimated undiscounted future benefit payments are expected to be $2.1 million in 2019, $2.0 million in 2020, $2.0 million in 2021, $2.0 million in 2022, $2.0 million in 2023 and $9.7 million in 2024 through 2028. Defined Contribution Retirement Plans The Company offers participation in the INTL FCStone Inc. 401(k) Plan (“401(k) Plan”), a defined contribution plan providing retirement benefits to all domestic full-time non-temporary employees who have reached 21 years of age. Employees may contribute from 1% to 80% of their annual compensation to the 401(k) Plan, limited to a maximum annual amount as set periodically by the Internal Revenue Service. The Company makes matching contributions to the 401(k) Plan in an amount equal to 62.5% of each participant’s eligible elective deferral contribution to the 401(k) Plan, up to 8% of employee compensation. Matching contributions vest, by participant, based on the following years of service schedule: less than two years – none, after two years – 33% , after three years – 66% , and after four years – 100% . U.K. based employees of INTL FCStone are eligible to participate in a defined contribution pension plan. The Company contributes double the employee’s contribution up to 10% of total base salary for this plan. For this plan, employees are 100% vested in both the employee and employer contributions at all times. For fiscal years ended September 30, 2018, 2017, and 2016 , the Company’s contribution to these defined contribution plans were $6.8 million , $6.1 million and $5.3 million , respectively.

Other Expenses (Notes)

Other Expenses (Notes)	12 Months Ended
	Sep. 30, 2018
Other Expenses [Abstract]
Other Expenses [Text Block]	Other Expenses Other expenses for the years ended September 30, 2018, 2017, and 2016 are comprised of the following: Year Ended September 30, (in millions) 2018 2017 2016 Contingent consideration, net (1) $ — $ 0.1 $ 0.4 Insurance 2.6 2.7 2.1 Advertising, meetings and conferences 6.2 4.0 5.1 Office supplies and printing 1.7 2.1 1.2 Other clearing related expenses 2.5 2.6 1.3 Other non-income taxes 4.9 4.6 4.3 Other 8.4 9.8 7.9 Total other expenses $ 26.3 $ 25.9 $ 22.3 (1) Contingent consideration includes remeasurement of contingent liabilities related to business combinations accounted for in accordance with the provisions of the Business Combinations Topic of the ASC (see Note 3 ).

Bad Debt on Physical Coal Bad D

Bad Debt on Physical Coal Bad Debt on Physical Coal (Notes)	12 Months Ended
	Sep. 30, 2018
Bad Debt on Physical Coal [Abstract]
Unusual or Infrequent Items, or Both, Disclosure [Text Block]	Note 17 – Bad Debt on Physical Coal During the first quarter of fiscal 2018 and the fourth quarter of fiscal 2017, the Company recorded charges to earnings of $1.0 million and $47.0 million , respectively, to record an allowance for doubtful accounts related to a bad debt incurred in the physical coal business, conducted solely in the Company’s Singapore subsidiary, INTL Asia Pte. Ltd., with a coal supplier. Components of the bad debt on physical coal include allowances on amounts due to the Company from the supplier related to: coal paid for but not delivered to clients; reimbursement of demurrage claims, dead freight and other charges paid by INTL Asia Pte. Ltd. to its clients; reimbursement due for deficiencies in the quality of coal delivered to clients; and losses incurred related to the cancellation of open sales contracts. During fiscal 2017, the Company purchased coal delivered onto barges and paid 80% of the value against bills of lading and purchase invoices, with the remaining 20% payable following inspection upon delivery to clients’ vessels. The Company took title of the coal when it was loaded onto barges and maintained title until it was offloaded onto clients’ vessels. The logistics related to the delivery of coal to the clients’ vessels was out-sourced to the Company’s coal supplier, and the Company determined that certain purchased coal was not delivered to the clients’ vessels during the fourth quarter ended September 30, 2017. Furthermore, the Company determined that the supplier was unable to deliver such purchased coal to its clients. Demurrage claims, dead freight, and other penalty charges paid and payable by INTL Asia Pte. Ltd. to its clients were due to be reimbursed by the supplier based on transaction agreements with the supplier. The Company determined the supplier was unable to make this reimbursement. The Company received an acknowledgment of debt and a note from the supplier, however, there is substantial uncertainty as to whether the supplier will be able to meet its financial obligations to the Company and as to the timing of any recovery. The Company continues to pursue all legal avenues available to it regarding this matter. The bad debt on physical coal is presented separately as a component of income before tax in the consolidated income statements. The Company has completed its exit of the physical coal business, which was part of our Physical Commodities segment and was conducted solely in INTL Asia Pte. Ltd. On November 22, 2018, the Company reached a settlement with a client, paying $5.1 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 accordingly the Company will record a recovery on the bad debt on physical coal of $1.7 million in the three months ending December 31, 2018.

Income Taxes (Notes)

Income Taxes (Notes)	12 Months Ended
	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Income Tax Disclosure [Text Block]	Income Taxes Effects of the Tax Cuts and Jobs Act On December 22, 2017, the President of the United States (“ U.S. ”) signed and enacted into law H.R. 1, the Tax Cuts and Jobs Act (the “Tax Reform”). Among the significant changes to the U.S. Internal Revenue Code, the Tax Reform lowers the U.S. federal corporate income tax rate from 35% to 21%, effective January 1, 2018. The Company computed income tax expense for the year ended September 30, 2018 using a U.S. statutory tax rate of 24.5% . The 21% U.S. statutory tax rate will apply to fiscal years ending September 30, 2019 and thereafter. The Tax Reform also imposes a one-time mandatory repatriation transition tax on previously untaxed accumulated and current earnings and profits (“E&P”) of certain foreign subsidiaries. The SEC staff issued Staff Accounting Bulletin No. 118 (“SAB 118”), which provides guidance on accounting for the tax effects of the Tax Reform. SAB 118 provides a measurement period that should not extend beyond one year from the Tax Reform enactment date for companies to complete the accounting under Accounting Standards Codification (“ASC”) 740 - Income Taxes (“ASC 740”). In accordance with SAB 118, a company must reflect the income tax effects of those aspects of the Tax Reform for which the accounting under ASC 740 is complete. To the extent that a company’s accounting for certain income tax effects of the Tax Reform is incomplete but it can determine a reasonable estimate, it must record a provisional estimate in the financial statements. If a company cannot determine a provisional estimate to be included in the financial statements, it should continue to apply ASC 740 based on the tax laws that were in effect immediately before the enactment of the Tax Reform. The accounting for certain elements of the Tax Reform is incomplete. However, as of September 30, 2018, the accounting for the remeasurement of the deferred tax assets and liabilities is complete. The remeasurement of the deferred tax assets and liabilities resulted in $8.6 million of income tax expense, which increased the effective tax rate by 8.5% during the year ended September 30, 2018. To determine the amount of the mandatory repatriation transition tax, the Company must determine, in addition to other factors, the amount of post 1986 E&P of the relevant subsidiaries, as well as the amount of non- U.S. income taxes paid on such earnings. The Company made a reasonable estimate of the mandatory repatriation transition tax and recorded a provisional transition tax obligation of $11.2 million , which increased the effective tax rate by 11% during the year ended September 30, 2018. While the Company can make reasonable estimates for the deemed repatriation transition tax, the final tax impact may differ from these estimates, due to, among other things, changes in our interpretations and assumptions, additional guidance that may be issued by taxing authorities, and actions the Company may take. The Tax Reform also establishes new tax laws that will affect the fiscal year ending September 30, 2019, including, but not limited to, (1) elimination of the corporate alternative minimum tax, (2) a new provision designed to tax global intangible low-taxed income (GILTI), (3) limitations on the utilization of net operating losses incurred in tax years beginning after September 30, 2018 to 80% of taxable income per tax year, (4) the creation of the base erosion anti-abuse tax (BEAT), (5) a general elimination of U.S. federal income taxes on dividends from foreign subsidiaries, and (6) limitations on the deductibility of interest expense and certain executive compensation. The Company has not yet determined the potential tax impact of provisions that are not yet effective, such as GILTI, BEAT, and the elimination of U.S. tax on dividends of future foreign earnings. The Company expects to make the policy election to treat GILTI as a period expense in the first quarter of fiscal year 2019. Income tax expense (benefit) for the years ended September 30, 2018, 2017, and 2016 was allocated as follows: Year Ended September 30, (in millions) 2018 2017 2016 Income tax expense attributable to income from operations $ 46.0 $ 8.8 $ 18.0 Taxes allocated to stockholders’ equity, related to pension liabilities 0.1 1.0 0.2 Taxes allocated to additional paid-in capital, related to share-based compensation — 0.1 (0.8 ) Total income tax expense $ 46.1 $ 9.9 $ 17.4 The components of income tax expense (benefit) attributable to income from operations were as follows: Year Ended September 30, (in millions) 2018 2017 2016 Current taxes: U.S. federal $ 0.8 $ 0.7 $ 1.3 U.S. State and local 0.5 1.2 0.8 International 22.4 16.7 16.8 Total current taxes 23.7 18.6 18.9 Deferred taxes 22.3 (9.8 ) (0.8 ) Income tax benefit attributable to interest income — — (0.1 ) Income tax expense $ 46.0 $ 8.8 $ 18.0 U.S. and international components of (loss) income from operations, before tax, was as follows: Year Ended September 30, (in millions) 2018 2017 2016 U.S. $ 9.9 $ (13.9 ) $ 4.8 International 91.6 29.1 67.9 Income from operations, before tax $ 101.5 $ 15.2 $ 72.7 Items accounting for the difference between income taxes computed at the federal statutory rate and income tax expense were as follows: Year Ended September 30, 2018 2017 2016 Federal statutory rate effect of: 24.5 % 35.0 % 35.0 % U.S. State and local income taxes 0.8 % (2.6 )% 1.3 % Foreign earnings and losses taxed at lower rates (0.8 )% 11.5 % (11.0 )% Change in foreign valuation allowance (0.8 )% (1.4 )% (0.3 )% Change in state valuation allowance — % 4.1 % — % U.S. permanent items (0.2 )% 3.6 % 0.8 % Foreign permanent items 2.1 % 8.1 % 1.9 % U.S. bargain purchase gain — % — % (3.0 )% Remeasurement of deferred tax 8.5 % — % — % Repatriation Transition tax 11.0 % — % — % Other reconciling items 0.2 % (0.6 )% 0.3 % Effective rate 45.3 % 57.7 % 25.0 % The components of deferred income tax assets and liabilities were as follows: (in millions) September 30, 2018 September 30, 2017 Deferred tax assets: Share-based compensation $ 2.8 $ 3.7 Pension liability — 0.1 Deferred compensation 1.4 2.0 Foreign net operating loss carryforwards 4.2 5.6 U.S. State and local net operating loss carryforwards 8.7 6.6 U.S. federal net operating loss carryforwards — 21.9 Intangible assets 1.8 6.1 Bad debt reserve 1.5 1.4 Tax credit carryforwards — 1.6 Foreign tax credit carryforwards 6.5 — Other compensation 3.4 3.6 Other 0.9 1.9 Total gross deferred tax assets 31.2 54.5 Less valuation allowance (3.5 ) (4.0 ) Deferred tax assets 27.7 50.5 Deferred income tax liabilities: Unrealized gain on securities 2.6 3.2 Prepaid expenses 1.8 2.5 Property and equipment 3.1 2.2 Pension liability 0.4 — Deferred income tax liabilities 7.9 7.9 Deferred income taxes, net $ 19.8 $ 42.6 Deferred income tax balances reflect the effects of temporary differences between the carrying amounts of assets and liabilities and their tax bases and are stated at enacted tax rates expected to be in effect when taxes are actually paid or recovered. As of September 30, 2018 and 2017 , the Company has net operating loss carryforwards for U.S. federal, state, local, and foreign income tax purposes of $9.4 million and $30.1 million , net of valuation allowances, respectively, which are available to offset future taxable income in these jurisdictions. The Company utilized the $21.9 million U.S. federal net operating loss in the current year against the mandatory repatriation transition tax. The state and local net operating loss carryforwards of $5.7 million , net of valuation allowance, begin to expire after September 2020. INTL Asia Pte. Ltd. has a net operating loss carryforward of $2.9 million . This Singapore net operating loss has an indefinite carryforward and, in the judgment of management, is more likely than not to be realized. As a result of Tax Reform, the AMT credit carryforward deferred tax asset has been reclassified to income taxes receivable. The Company can continue to utilize AMT credits to offset regular income tax liability in fiscal years 2019 through 2021. Any remaining amount is fully refundable by fiscal year 2022. In the current year, the Company generated $6.5 million in foreign tax credit carryforwards as part of the mandatory repatriation transition tax. These credits expire in fiscal year 2028. In the judgment of management, the Company believes that sufficient taxable income will be earned to utilize the foreign tax credit carryforwards within 10 years. The valuation allowance for deferred tax assets as of September 30, 2018 was $3.5 million . The net change in the total valuation allowance for the year ended September 30, 2018 was a decrease of $0.5 million . The valuation allowances as of September 30, 2018 and 2017 were primarily related to U.S. state and local and foreign net operating loss carryforwards that, in the judgment of management, are not more likely than not to be realized. The Company incurred U.S. federal, state, and local taxable losses for the years ended September 30, 2018 (excluding the taxable income associated with the mandatory repatriation transition tax), 2017, and 2016 of $(3.7) million , $(20.5) million , and $(9.7) million , respectively. The differences between actual levels of past taxable losses and pre-tax book income (losses) are primarily attributable to temporary differences in these jurisdictions, such as tax deductible amortization and bonus depreciation. When evaluating if U.S. federal, state, and local deferred taxes are realizable, the Company considered deferred tax liabilities of $5.0 million that are scheduled to reverse from 2019 to 2021 and $2.5 million of deferred tax liabilities associated with unrealized gains in securities which the Company could sell, if necessary. Furthermore, the Company considered its ability to implement business and tax planning strategies that would allow the remaining U.S. federal, state, and local deferred tax assets, net of valuation allowances, to be realized in less than 5 years. Based on the tax planning strategies that can be implemented, management believes that it is more likely than not that the Company will realize the tax benefit of the deferred tax assets, net of the existing valuation allowance, in the future. The total amount of undistributed earnings in the Company’s foreign subsidiaries, for income tax purposes, was $354.7 million as of September 30, 2018. The Company recognized the mandatory repatriation tax related to these undistributed earnings as part of Tax Reform and, as a result, repatriation of these amounts would not be subject to additional U.S. federal income tax but may be subject to applicable withholding taxes in the relevant jurisdictions. The Company’s intent is to permanently reinvest these funds outside of the United States, with the exception of $13.0 million that will be distributed in fiscal year 2019. Foreign withholding tax is not applicable to this distribution. A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows: Year Ended September 30, (in millions) 2018 2017 2016 Balance, beginning of year $ 0.1 $ 0.1 $ — Gross increases for tax positions related to prior years — — 0.1 Balance, end of year $ 0.1 $ 0.1 $ 0.1 The Company has a minimal balance of unrecognized tax benefits as of September 30, 2018 , that, if recognized, would affect the effective tax rate. While it is expected that the amount of unrecognized tax benefits will change in the next twelve months, the Company does not expect this change to have a material impact on the results of operations or the financial position of the Company. Accrued interest and penalties are included in the related tax liability line in the consolidated balance sheets. The Company had no accrued interest and penalties included in the consolidated balance sheets as of September 30, 2018 and 2017 . The Company recognizes accrued interest and penalties related to income taxes as a component of income tax expense. The Company had no amount of interest, net of federal benefit, and penalties recognized as a component of income tax expense during the years ended September 30, 2018, 2017, and 2016 . The Company and its subsidiaries file income tax returns with the U.S. federal jurisdiction and various U.S. state and local and foreign jurisdictions. The Company has open tax years ranging from September 30, 2010 through September 30, 2018 with U.S. federal and state and local taxing authorities. In the U.K., the Company has open tax years ending September 30, 2017 to September 30, 2018. In Brazil, the Company has open tax years ranging from December 31, 2013 through December 31, 2017. In Argentina, the Company has open tax years ranging from September 30, 2011 to September 30, 2018. In Singapore, the Company has open tax years ranging from September 30, 2014 to September 30, 2018.

Acquisitions (Notes)

Acquisitions (Notes)	12 Months Ended
	Sep. 30, 2018
Business Combinations [Abstract]
Business Combination Disclosure [Text Block]	Acquisitions The Company’s consolidated financial statements include the operating results of the acquired businesses from the dates of acquisition. Acquisitions in Fiscal 2018 PayCommerce Financial Solutions, LLC On September 5, 2018, the Company acquired all of the outstanding membership interests of PayCommerce Financial Solutions, LLC (“PCFS”). Subsequent to the acquisition, the Company renamed PCFS to INTL Technology Services, LLC (“ITS”). ITS is a fully accredited SWIFT Service Bureau provider. This acquisition enables the Company to act as a SWIFT Service Bureau for its 300-plus correspondent banking network, thus providing another important service for delivering local currency, cross-border payments to the developing world. The purchase price was approximately $3.8 million of cash consideration. The purchase price allocation resulted in $0.7 million in receivables, $0.8 million in property, plant, and equipment, $0.5 million in equity investments, and $2.2 million in liabilities assumed. Additionally, the Company acquired identifiable, definite lived client relationship and client list assets that have been assigned a fair value of $1.3 million and a useful life of 5 years. The fair value of the consideration transferred exceeded the fair value of identifiable assets acquired and liabilities assumed. The excess of the purchase consideration over the fair value of net tangible and identifiable intangible assets acquired of $2.6 million was recorded as goodwill. Management believes that the goodwill represents the synergies expected from the incremental revenue that can be realized from combining the technologies acquired with the Company’s pre-existing correspondent banking network. The estimated fair value assigned to the tangible assets, identifiable intangible assets, and assumed liabilities were based on management’s estimates and assumptions. This business has been included within the Company’s Global Payments Segment. The Company’s consolidated income statement for the year ended September 30, 2018 includes the post-acquisition results of ITS, which was immaterial in relation to the Company’s consolidated results. Carl Kliem S.A. On June 12, 2018, the Company executed a sale and purchase agreement to acquire the entire issued and outstanding share capital of Carl Kliem S.A. Carl Kliem S.A. is an independent interdealer broker based in Luxembourg, a leading European financial hub, which provides foreign exchange, interest rate and fixed income products to a diverse, institutional client base across the European Union. Carl Kliem S.A. employs approximately 40 people and has over 400 active institutional clients. This acquisition is expected to provide the Company with a strong European client base and a European Union based footprint following the completion of Brexit. The closing of the agreement was conditional upon approval of the Luxembourg financial sector supervisory authority, the Commission de Surveillance du Secteur Financier (“CSSF”). In November 2018, the Company received regulatory approval from the CSSF to complete the acquisition and the acquisition closed effective November 30, 2018. The purchase price is equal to the net tangible book value on the closing date minus restructuring costs and is not material to the Company. The initial accounting for the purchase price allocation is not yet complete. Acquisition in Fiscal 2017 ICAP’s EMEA Oils Broking Business Effective October 1, 2016, the Company’s subsidiary, INTL FCStone Ltd acquired the London-based EMEA oils business of ICAP Plc. The business included more than 30 front office employees across the fuel, crude, middle distillates, futures and options desks that have relationships with more than 200 commercial and institutional clients throughout Europe, the Middle East and Africa. The terms of the agreement included cash consideration of $6.0 million paid directly to ICAP as well as incentive amounts payable to employees acquired based upon their continued employment. The cash consideration paid to ICAP was dependent upon the number of brokers who accepted INTL FCStone Ltd’s employment offer. The transaction was accounted for as an asset acquisition in accordance with FASB ASC 805-50 and FASB ASC 350. The cash consideration paid was allocated entirely to the intangible asset recognized related to the client base acquired. The intangible asset was assigned to the Clearing and Execution Services segment and will be amortized over a useful life of 5 years. Acquisition in Fiscal 2016 Sterne Agee Effective July 1, 2016 , the Company acquired all of the equity interests of Sterne Agee, LLC’s (a wholly-owned subsidiary of Stifel Financial Corp.) legacy independent brokerage and clearing businesses, Sterne Agee & Leach, Inc.; Sterne Agee Clearing, Inc.; Sterne Agee Financial Services, Inc. Effective August 1, 2016 , the Company acquired all of the equity interests of Sterne Agee, LLC’s legacy Registered Investment Advisor (“RIA”) business, Sterne Agee Asset Management, Inc. and Sterne Agee Investment Advisor Services, Inc. - collectively (“Sterne Agee”) for cash consideration. Effective July 1, 2017, Sterne Agee & Leach, Inc. was merged into the Company’s wholly-owned regulated U.S. subsidiary, INTL FCStone Financial. Additionally, during 2017, Sterne Agee Clearing, Inc., Sterne Agee Financial Services, Inc., Sterne Agee Asset Management, Inc., and Sterne Agee Investment Advisor Services, Inc. were renamed INTL Custody & Clearing Solutions, Inc., SA Stone Wealth Management, Inc., INTL Advisory Consultants, Inc., and SA Stone Investment Advisors, Inc., respectively. The acquisition-date fair value of the consideration transferred totaled $45.0 million . The purchase price allocation resulted in $24.9 million in cash, $151.6 million in receivables, $5.7 million in deferred tax assets, $4.8 million in other assets and $136.0 million in liabilities assumed. The fair value of identifiable assets acquired and liabilities assumed exceeded the fair value of the consideration transferred. Consequently, the Company reassessed the recognition and measurement of identifiable assets acquired and liabilities assumed and concluded that all acquired assets and assumed liabilities were recognized and that the valuation procedures and resulting measures were appropriate. As a result, the Company recognized a gain of $6.2 million for the year ended September 30, 2016, which is included in the line item ‘Other gains’ in the consolidated income statement. The Company believes the transaction resulted in a gain primarily due to the Company’s ability to incorporate these business activities into its existing business structure, and its ability to utilize certain deferred tax assets and other assets while operating the business that may not have been likely to be realized by the seller. There were no purchase price adjustments recorded during the measurement period and the purchase price allocation is now considered final. The businesses have been included within the Company’s Clearing and Execution Services Segment. The Company’s consolidated income statement for the year ended September 30, 2016 includes the post-acquisition results of the Sterne Agee businesses, which were immaterial. The acquired businesses contributed net operating revenues of $8.6 million and net loss of $0.1 million to the Company for the period from July 1, 2016 to September 30, 2016.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Loss) (Notes)	12 Months Ended
	Sep. 30, 2018
Accumulated Other Comprehensive Income (Loss) [Abstract]
Comprehensive Income (Loss) Note [Text Block]	Accumulated Other Comprehensive (Loss) Income Comprehensive income consists of net income and other gains and losses affecting stockholders’ equity that, under U.S. GAAP, are excluded from net income. Other comprehensive (loss) income includes net actuarial gains from defined benefit pension plans and losses on foreign currency translations. The following table summarizes the changes in accumulated other comprehensive (loss) income for the year ended September 30, 2018 . (in millions) Foreign Currency Translation Adjustment Pension Benefits Adjustment Accumulated Other Comprehensive Loss Balances as of September 30, 2017 $ (21.5 ) $ (3.0 ) $ (24.5 ) Other comprehensive (loss) income, net of tax before reclassifications (9.0 ) 0.3 (8.7 ) Amounts reclassified from AOCI, net of tax — 0.1 0.1 Other comprehensive (loss) income, net of tax (9.0 ) 0.4 (8.6 ) Balances as of September 30, 2018 $ (30.5 ) $ (2.6 ) $ (33.1 )

Quarterly Financial Information

Quarterly Financial Information (Unaudited) (Notes)	12 Months Ended
	Sep. 30, 2018
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Information [Text Block]	Quarterly Financial Information (Unaudited) The Company has set forth certain quarterly unaudited financial data for the past two years in the tables below: For the 2018 Fiscal Quarter Ended (in millions, except per share amounts) September 30 (1) June 30 March 31 December 31 Total revenues $ 6,078.8 $ 7,118.3 $ 6,507.0 $ 7,918.6 Cost of sales of physical commodities 5,835.6 6,858.5 6,246.8 7,706.0 Operating revenues 243.2 259.8 260.2 212.6 Transaction-based clearing expenses 43.1 49.0 50.7 36.9 Introducing broker commissions 32.4 34.1 36.2 31.1 Interest expense 25.3 22.1 19.0 14.3 Net operating revenues 142.4 154.6 154.3 130.3 Compensation and benefits 85.4 86.9 88.2 77.2 Bad debts 1.2 1.6 0.2 0.1 Bad debt on physical coal (1) — — — 1.0 Other expenses 35.3 35.2 36.4 33.4 Total compensation and other expenses 121.9 123.7 124.8 111.7 Other gain — 2.0 — — Income before tax 20.5 32.9 29.5 18.6 Income tax expense 4.8 8.9 6.8 25.5 Net income (loss) $ 15.7 $ 24.0 $ 22.7 $ (6.9 ) Net basic earnings (loss) per share $ 0.83 $ 1.27 $ 1.20 $ (0.37 ) Net diluted earnings (loss) per share $ 0.81 $ 1.25 $ 1.18 $ (0.37 ) For the 2017 Fiscal Quarter Ended (in millions, except per share amounts) September 30 June 30 March 31 December 31 Total revenues $ 12,382.5 $ 5,505.9 $ 5,460.8 $ 6,074.4 Cost of sales of physical commodities 12,177.4 5,308.3 5,265.0 5,888.9 Operating revenues 205.1 197.6 195.8 185.5 Transaction-based clearing expenses 35.1 33.9 33.7 33.6 Introducing broker commissions 26.9 29.2 28.2 28.7 Interest expense 12.0 11.2 10.0 8.9 Net operating revenues 131.1 123.3 123.9 114.3 Compensation and benefits 73.0 75.5 76.6 70.6 Bad debts 0.4 0.1 1.3 2.5 Bad debt on physical coal (1) 47.0 — — — Other expenses 33.2 32.7 31.7 32.8 Total compensation and other expenses 153.6 108.3 109.6 105.9 Income before tax (22.5 ) 15.0 14.3 8.4 Income tax expense 1.1 2.3 3.3 2.1 Net income $ (23.6 ) $ 12.7 $ 11.0 $ 6.3 Net basic (loss) earnings per share $ (1.27 ) $ 0.67 $ 0.58 $ 0.34 Net diluted (loss) earnings per share $ (1.27 ) $ 0.66 $ 0.58 $ 0.34 (1) During the first quarter of fiscal 2018 and the fourth quarter of fiscal 2017, the Company recorded charges to earnings of $1.0 million and $47.0 million , respectively, to record an allowance for doubtful accounts related to a bad debt incurred in the physical coal business conducted solely in INTL Asia Pte. Ltd., with a coal supplier, as further discussed in Note 17 .

Segment and Geographic Informat

Segment and Geographic Information (Notes)	12 Months Ended
	Sep. 30, 2018
Segment Analysis [Abstract]
Segment Reporting Disclosure [Text Block]	Segment and Geographic Information The Company reports its operating segments based on services provided to clients. The Company’s business activities are managed as operating segments and organized into reportable segments as follows: • Commercial Hedging ( includes components Financial Agricultural (Ag) & Energy and LME Metals) • Global Payments • Securities (includes components Equity Capital Markets (formerly referred to as Equity Market-Making), Debt Capital Markets (which now includes both our Debt Trading and Investment Banking businesses discussed in prior fiscal years) and Asset Management) • Physical Commodities (includes components Precious Metals and Physical Ag & Energy) • Clearing and Execution Services (includes components Exchange-Traded Futures and Options, FX Prime Brokerage, Correspondent Clearing, Independent Wealth Management, and Derivative Voice Brokerage) Commercial Hedging The Company serves its commercial clients through its team of risk management consultants, providing a high-value-added service that it believes differentiates the Company from its competitors and maximizes the opportunity to retain clients. The Company’s risk management consulting services are designed to quantify and monitor commercial entities’ exposure to commodity and financial risk. Upon assessing this exposure, the Company develops a plan to control and hedge these risks with post-trade reporting against specific client objectives. Clients are assisted in the execution of their hedging strategies through a wide range of products from listed exchange-traded futures and options, to basic OTC instruments that offer greater flexibility, to structured OTC products designed for customized solutions. The Company’s services span virtually all traded commodity markets, with the largest concentrations in agricultural and energy commodities (consisting primarily of grains, energy and renewable fuels, coffee, sugar, cotton, and food service) and base metals products listed on the LME. The Company’s base metals business includes a position as a Category One ring dealing member of the LME, providing execution, clearing and advisory services in exchange-traded futures and OTC products. The Company also provides execution of foreign currency forwards and options and interest rate swaps as well as a wide range of structured product solutions to commercial clients who are seeking cost-effective hedging strategies. Generally, clients direct their own trading activity and the Company’s risk management consultants do not have discretionary authority to transact trades on behalf of clients. Global Payments The Company provides global payment solutions to banks and commercial businesses as well as charities and non-governmental organizations and government organizations. The Company offers payments services in more than 170 countries and 140 currencies, which it believes is more than any other payments solution provider, and provides competitive and transparent pricing. Its proprietary FXecute global payments platform is integrated with a financial information exchange (“FIX”) protocol. This FIX protocol is an electronic communication method for the real-time exchange of information, and the Company believes it represents one of the first FIX offerings for cross-border payments in exotic currencies. FIX functionality allows clients to view real time market rates for various currencies, execute and manage orders in real-time, and view the status of their payments through the easy-to-use portal. Additionally, as a member of the Society for Worldwide Interbank Financial Telecommunication (“SWIFT”), the Company is able to offer its services to large money center and global banks seeking more competitive international payments services. Through this single comprehensive platform and our commitment to client service, the Company believes it is able to provide simple and fast execution, ensuring delivery of funds in any of these countries quickly through its global network of approximately 300 correspondent banks. In this business, the Company primarily acts as a principal in buying and selling foreign currencies on a spot basis. The Company derives revenue from the difference between the purchase and sale prices. The Company believes its clients value its ability to provide exchange rates that are significantly more competitive than those offered by large international banks, a competitive advantage that stems from its years of foreign exchange expertise focused on smaller, less liquid currencies. Securities The Company provides value-added solutions that facilitate cross-border trading and believes its clients value the Company’s ability to manage complex transactions, including foreign exchange, utilizing its local understanding of market convention, liquidity and settlement protocols around the world. The Company’s clients include U.S.-based regional and national broker-dealers and institutions investing or executing client transactions in international markets and foreign institutions seeking access to the U.S. securities markets. The Company is one of the leading market makers in foreign securities, including unlisted ADRs, GDRs and foreign ordinary shares. The Company makes markets in over 5,000 ADRs, GDRs and foreign ordinary shares, of which over 3,600 trade in the OTC market. In addition, it will, on request, make prices in more than 10,000 unlisted foreign securities. The Company is also a broker-dealer in Argentina where we are active in providing institutional executions in the local capital markets. The Company acts as an institutional dealer in fixed income securities, including U.S. Treasury, U.S. government agency, agency mortgage-backed and asset-backed securities to a client base including asset managers, commercial bank trust and investment departments, broker-dealers and insurance companies. The Company also originates, structures and places debt instruments in the international and domestic capital markets. These instruments include complex asset-backed securities (primarily in Argentina) and domestic municipal securities. On occasion, the Company may invest its own capital in debt instruments before selling them. The Company also actively trades in a variety of international debt instruments and operates an asset management business in which it earns fees, commissions and other revenues for management of third party assets and investment gains or losses on its investments in funds and proprietary accounts managed either by its investment managers or by independent investment managers. Physical Commodities This segment consists of the Company’s physical Precious Metals trading and Physical Agricultural and Energy commodity businesses. In Precious Metals, the Company provides a full range of trading and hedging capabilities, including OTC products, to select producers, consumers, and investors. In the Company’s trading activities, it acts as a principal, committing its own capital to buy and sell precious metals on a spot and forward basis. In the Company’s Physical Ag & Energy commodity business, it acts as a principal to facilitate financing, structured pricing and logistics services to clients across the commodity complex, including energy commodities, grains, oil seeds, cotton, coffee, cocoa, edible oils and feed products. The Company provides financing to commercial commodity-related companies against physical inventories. The Company uses sale and repurchase agreements to purchase commodities evidenced by warehouse receipts, subject to a simultaneous agreement to sell such commodities back to the original seller at a later date. Transactions where the sale and repurchase price are fixed upon execution, and meet additional required conditions, are accounted for as product financing arrangements, and accordingly no commodity inventory, purchases or sales are recorded. Transactions where the repurchase price is not fixed at execution do not meet all the criteria to be accounted for as product financing arrangements, and therefore are recorded as commodity inventory, purchases and sales. INTL FCStone Ltd precious metals sales and cost of sales are presented on a net basis and included as a component of ‘trading gains, net’ in the consolidated income statements, in accordance with U.S GAAP accounting requirements for broker-dealers. Precious metals sales and cost of sales for subsidiaries that are not broker-dealers continue to be recorded on a gross basis. Precious metals inventory held by subsidiaries that are not broker-dealers continues to be valued at the lower of cost or market value. Precious metals sales and cost of sales for subsidiaries that are not broker-dealers continue to be recorded on a gross basis. The agricultural commodity inventories are carried at net realizable value, which approximates fair value less disposal costs. The agricultural inventories have reliable, readily determinable and realizable market prices, have relatively insignificant costs of disposal and are available for immediate delivery. The Company records its Physical Ag & Energy commodities revenues on a gross basis. Operating revenues and losses from its precious metals commodities derivatives activities are included in ‘trading gains, net’ in the consolidated income statements. Operating revenues and losses from our Physical Ag and Energy commodity business are included in ‘cost of sales of physical commodities’ in the consolidated income statements The Company generally mitigates the price risk associated with commodities held in inventory through the use of derivatives. The Company does not elect hedge accounting under U.S. GAAP in accounting for this price risk mitigation. The Company’s management continues to evaluate performance and allocated resources on an operating revenue basis. Clearing and Execution Services (CES) The Company provides competitive and efficient clearing and execution in all major futures and securities exchanges globally as well as prime brokerage in major foreign currency pairs and swap transactions. Through its platform, client orders are accepted and directed to the appropriate exchange for execution. The Company then facilitates the clearing of clients’ transactions. Clearing involves the matching of clients’ trades with the exchange, the collection and management of client margin deposits to support the transactions, and the accounting and reporting of the transactions to clients. As of September 30, 2018 , the Company held $2.6 billion in required client segregated assets, which it believes makes it the third largest independent futures commission merchant (“FCM”) in the U.S. not affiliated with a major financial institution or commodity intermediary, end-user or producer, as measured by required client segregated assets. The Company seeks to leverage its capabilities and capacity by offering facilities management or outsourcing solutions to other FCM’s. The Company is an independent full-service provider to introducing broker-dealers (“IBD’s”) of clearing, custody, research, syndicated and security-based lending products and services, including a proprietary technology platform which offers seamless connectivity to ensure a positive client experience through the clearing and settlement process. The Company’s independent wealth management business, which offers a comprehensive product suite to retail clients nationwide, clears through this platform. The Company believes it is one of the leading mid-market clearer’s in the securities industry, with approximately 60 correspondent clearing relationships with over $15 billion in assets under management or administration as of September 30, 2018 . Within this segment, the Company also maintains what it believes is one of the largest non-bank prime brokers and swap dealers in the world. Through this offering, the Company provides prime brokerage foreign exchange (“FX”) services to financial institutions and professional traders. The Company provides its clients with the full range of OTC products, including 24-hour a day execution of spot, forwards and options as well as non-deliverable forwards in both liquid and exotic currencies. The Company also operate a proprietary foreign exchange desk that arbitrages the exchange-traded foreign exchange markets with the cash markets. Through its London-based Europe, Middle East and Africa (“EMEA”) oil voice brokerage business, the Company employs over 30 employees providing brokerage services across the fuel, crude and middle distillates markets with over 200 well known commercial and institutional clients throughout Europe, the Middle East and Africa. ******** The total revenues reported combine gross revenues for the physical commodities business and net revenues for all other businesses. In order to reflect the way that the Company’s management views the results, the tables below also reflect the segment contribution to ‘operating revenues’, which is shown on the face of the consolidated income statements and which is calculated by deducting physical commodities cost of sales from total revenues. Segment data includes the profitability measure of net contribution by segment. Net contribution is one of the key measures used by management to assess the performance of each segment and for decisions regarding the allocation of the Company’s resources. Net contribution is calculated as revenue less direct cost of sales, transaction-based clearing expenses, variable compensation, introducing broker commissions, and interest expense. Variable compensation paid to risk management consultants/traders generally represents a fixed percentage of an amount equal to revenues generated, and in some cases, revenues produced less transaction-based clearing charges, base salaries and an overhead allocation. Segment data also includes segment income which is calculated as net contribution less non-variable direct expenses of the segment. These non-variable direct expenses include trader base compensation and benefits, operational employee compensation and benefits, communication and data services, business development, professional fees, bad debts and other direct expenses. Inter-segment revenues, charges, receivables and payables are eliminated upon consolidation, except revenues and costs related to foreign currency transactions undertaken on an arm’s length basis by the foreign exchange trading business for the securities business. The foreign exchange trading business competes for this business as it does for any other business. If its rates are not competitive, the securities businesses buy or sell their foreign currency through other market counterparties. On a recurring basis, the Company sweeps excess cash from certain operating segments to a centralized corporate treasury function in exchange for an intercompany receivable asset. The intercompany receivable asset is eliminated during consolidation, and therefore this practice may impact reported total assets between segments. Information concerning operations in these segments of business is shown in accordance with the Segment Reporting Topic of the ASC as follows: Year Ended September 30, (in millions) 2018 2017 2016 Total revenues: Commercial Hedging $ 286.7 $ 244.6 $ 236.1 Global Payments 99.2 89.2 73.2 Securities 196.2 151.7 175.2 Physical Commodities 26,703.8 28,684.4 14,120.5 Clearing and Execution Services 332.4 259.8 151.1 Corporate unallocated 4.4 (6.1 ) (1.2 ) Total $ 27,622.7 $ 29,423.6 $ 14,754.9 Operating revenues (loss): Commercial Hedging $ 286.7 $ 244.6 $ 236.1 Global Payments 99.2 89.2 73.2 Securities 196.2 151.7 175.2 Physical Commodities 56.9 44.8 36.6 Clearing and Execution Services 332.4 259.8 151.1 Corporate unallocated 4.4 (6.1 ) (1.2 ) Total $ 975.8 $ 784.0 $ 671.0 Net operating revenues (loss): Commercial Hedging $ 226.4 $ 194.3 $ 188.2 Global Payments 93.5 80.6 65.3 Securities 94.6 94.6 121.9 Physical Commodities 44.8 37.3 31.5 Clearing and Execution Services 122.6 102.2 48.8 Corporate unallocated (0.3 ) (16.4 ) (11.8 ) Total $ 581.6 $ 492.6 $ 443.9 Net contribution: (Revenues less cost of sales, transaction-based clearing expenses, variable bonus compensation, introducing broker commissions and interest expense): Commercial Hedging $ 164.7 $ 141.8 $ 134.4 Global Payments 75.0 64.4 52.2 Securities 69.1 75.6 97.5 Physical Commodities 31.8 27.2 23.4 Clearing and Execution Services 91.8 78.0 39.5 Total $ 432.4 $ 387.0 $ 347.0 Segment income (loss): (Net contribution less non-variable direct segment costs): Commercial Hedging $ 96.4 $ 72.8 $ 68.7 Global Payments 59.8 50.6 39.8 Securities 40.8 46.6 69.4 Physical Commodities (1) 16.6 (31.4 ) 13.3 Clearing and Execution Services 48.3 30.4 14.8 Total $ 261.9 $ 169.0 $ 206.0 Reconciliation of segment income to income before tax: Segment income $ 261.9 $ 169.0 $ 206.0 Costs not allocated to operating segments (2) 162.4 153.8 139.5 Other gains 2.0 — 6.2 Income before tax $ 101.5 $ 15.2 $ 72.7 (1) During the first quarter of fiscal 2018 and the fourth quarter of fiscal 2017, the Company recorded charges to earnings of $1.0 million and $47.0 million , respectively, to record an allowance for doubtful accounts related to a bad debt incurred in the physical coal business conducted solely in INTL Asia Pte. Ltd., with a coal supplier, as further discussed in Note 17 . (2) The costs not allocated to operating segments include certain shared services such as information technology, accounting and treasury, credit and risk, legal and compliance, and human resources and other activities. (in millions) As of September 30, 2018 As of September 30, 2017 As of September 30, 2016 Total assets: Commercial Hedging $ 1,935.7 $ 1,650.3 $ 1,637.5 Global Payments 206.6 199.5 191.4 Securities 3,058.2 2,101.7 2,130.7 Physical Commodities 413.7 339.5 258.0 Clearing and Execution Services 2,109.9 1,818.9 1,617.4 Corporate unallocated 100.6 133.5 115.3 Total $ 7,824.7 $ 6,243.4 $ 5,950.3 Information regarding revenues and operating revenues for the years ended September 30, 2018, 2017, and 2016 , and information regarding long-lived assets (defined as property, equipment, leasehold improvements and software) as of September 30, 2018, 2017, and 2016 in geographic areas were as follows: Year Ended September 30, (in millions) 2018 2017 2016 Total revenues: United States $ 1,587.6 $ 1,168.0 $ 817.1 Europe 189.6 166.9 463.5 South America 59.5 53.9 64.8 Asia 25,781.4 28,030.3 13,405.1 Other 4.6 4.5 4.4 Total $ 27,622.7 $ 29,423.6 $ 14,754.9 Operating revenues: United States $ 695.3 $ 529.4 $ 457.0 Europe 189.0 166.9 120.2 South America 58.0 54.0 64.8 Asia 28.9 29.2 24.6 Other 4.6 4.5 4.4 Total $ 975.8 $ 784.0 $ 671.0 (in millions) As of September 30, 2018 As of September 30, 2017 As of September 30, 2016 Long-lived assets, as defined: United States $ 33.0 $ 29.7 $ 23.3 Europe 6.8 7.3 4.8 South America 1.4 1.5 1.2 Asia 1.2 0.2 0.1 Total $ 42.4 $ 38.7 $ 29.4

Condensed Parent Only Financial

Condensed Parent Only Financial Statements (Notes)	12 Months Ended
	Sep. 30, 2018
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Condensed Financial Information of Parent Company Only Disclosure [Text Block]	Schedule I INTL FCStone Inc. Condensed Balance Sheets Parent Company Only (in millions) September 30, September 30, ASSETS Cash and cash equivalents $ 1.8 $ 2.0 Receivable from subsidiaries, net 23.3 3.8 Notes receivable, net 1.8 4.8 Income taxes receivable 14.9 8.6 Investment in subsidiaries (1) 318.0 312.3 Financial instruments owned, at fair value 4.4 — Deferred income taxes, net 8.8 26.5 Property and equipment, net 25.9 24.8 Other assets 7.6 7.6 Total assets $ 406.5 $ 390.4 LIABILITIES AND EQUITY Liabilities: Accounts payable and other accrued liabilities $ 23.0 $ 19.8 Payable to clients 1.7 2.1 Payable to lenders under loans 209.4 152.0 Payable to subsidiaries, net — 49.4 Financial instruments sold, not yet purchased, at fair value 59.3 25.3 Total liabilities 293.4 248.6 Equity: INTL FCStone Inc. (Parent Company Only) stockholders’ equity: Preferred stock, $0.01 par value. Authorized 1,000,000 shares; no shares issued or outstanding — — Common stock, $0.01 par value. Authorized 30,000,000 shares; 21,030,497 issued and 18,908,540 outstanding at September 30, 2018 and 20,855,243 issued and 18,733,286 outstanding at September 30, 2017 0.2 0.2 Common stock in treasury, at cost - 2,121,957 shares at September 30, 2018 and 2017 (46.3 ) (46.3 ) Additional paid-in capital 267.5 259.0 Retained earnings (1) (108.3 ) (71.1 ) Total INTL FCStone Inc. (Parent Company Only) stockholders’ equity 113.1 141.8 Total liabilities and equity $ 406.5 $ 390.4 (1) Within the Condensed Balance Sheets and Condensed Statements of Operations of INTL FCStone Inc. - Parent Company Only, the Company has accounted for its investment in wholly owned subsidiaries using the cost method of accounting. Under this method, the Company’s share of the earnings or losses of such subsidiaries are not included in the Condensed Balance Sheet or Condensed Statements of Operations. If the accounting for its investment in wholly owned subsidiaries were presented under the equity method of accounting, investment in subsidiaries and retained earnings would each increase by $425.3 million as of September 30, 2018, respectively, and $332.6 million , as of September 30, 2017, respectively. Schedule I INTL FCStone Inc. Condensed Statements of Operations Parent Company Only Year Ended September 30, (in millions) 2018 2017 2016 Revenues: Management fees from affiliates $ 40.4 $ 39.1 $ 30.1 Trading (losses) gains, net — (1.0 ) 0.7 Consulting fees — — 2.2 Interest income 2.3 1.2 1.8 Dividend income from subsidiaries (2) 41.9 52.7 31.0 84.6 92.0 65.8 Interest expense 15.7 14.4 13.4 Net revenues 68.9 77.6 52.4 Non-interest expenses: Compensation and benefits 73.0 60.3 52.8 Clearing and related expenses 1.1 1.2 1.7 Introducing broker commissions — — 0.6 Trade systems and market information (3) 5.8 6.4 5.6 Occupancy and equipment rental 2.6 2.5 2.8 Professional fees 6.7 3.7 4.8 Travel and business development 2.6 2.7 1.7 Non-trading technology and support (3) 9.1 7.4 4.7 Depreciation and amortization 4.8 3.3 2.5 Communications (3) 0.9 0.9 1.1 Bad debts — — 0.2 Management services fees to affiliates — — 1.2 Other (3) 6.9 5.6 7.0 Total non-interest expenses 113.5 94.0 86.7 Gain on acquisition — — 6.2 Loss from operations, before tax (44.6 ) (16.4 ) (28.1 ) Income tax benefit 7.4 26.8 24.7 Net (loss) income $ (37.2 ) $ 10.4 $ (3.4 ) (2) W ithin the Condensed Balance Sheets and Condensed Statements of Operations of INTL FCStone Inc. - Parent Company Only, the Company has accounted for its investment in wholly owned subsidiaries using the cost method of accounting. Under this method, the Company’s share of the earnings or losses of such subsidiaries are not included in the Condensed Balance Sheet or Condensed Statements of Operations. If the accounting for its investment in wholly owned subsidiaries were presented under the equity method of accounting, revenues would include a loss from investment in subsidiaries of $4.0 million for the year ended September 30, 2017, and income from investment in subsidiaries of $92.7 million and $58.1 million for the years ended September 30, 2018 and 2016, respectively. (3) During the year ended September 30, 2018, the Company separately classified non-trading technology and support costs that were previously included within ‘Other’ on the Condensed Statements of Operations of INTL FCStone Inc. - Parent Company Only. Additionally, during the year ended September 30, 2018, the Company separately classified communications related expenses separately from trading systems and market information related costs. In performing these reclassifications, the Company has made immaterial, retrospective adjustments to conform to the current period presentation. For the years ended September 30, 2017 and 2016, ‘Other’ expenses included $7.4 million and $4.7 million , respectively, of expenses that are now included within ‘Non-trading technology and support’ on the Condensed Statements of Operations of INTL FCStone Inc. - Parent Company Only. For the years ended September 30, 2017 and 2016, ‘Trading systems and market information’ included $0.9 million and $1.1 million , respectively, of expenses that are now included within ‘Communications’ on the Condensed Statements of Operations of INTL FCStone Inc. - Parent Company Only. Schedule I INTL FCStone Inc. Condensed Statements of Cash Flows Parent Company Only Year Ended September 30, (in millions) 2018 2017 2016 Cash flows from operating activities: Net (loss) income $ (37.2 ) $ 10.4 $ (3.4 ) Adjustments to reconcile net (loss) income to net cash (used in) provided by operating activities: Depreciation and amortization 4.8 3.3 2.5 Provision for impairments — — 0.2 Deferred income taxes 18.0 (10.7 ) (3.3 ) Amortization and extinguishment of debt issuance costs 0.7 1.7 1.0 Amortization of share-based compensation expense 6.1 5.5 5.1 Gain on acquisition — — (6.2 ) Changes in operating assets and liabilities: Deposits and receivables from broker-dealers, clearing organizations, and counterparties — 2.9 (2.8 ) Receivables from subsidiaries, net (0.8 ) (0.3 ) (3.1 ) Due to/from subsidiaries (68.6 ) 27.0 (86.6 ) Notes receivable, net 2.9 2.1 39.1 Income taxes receivable (6.6 ) 5.4 10.3 Financial instruments owned, at fair value (4.4 ) 1.3 1.7 Other assets (0.7 ) 7.8 0.3 Accounts payable and other accrued liabilities 8.6 (7.8 ) 0.4 Payable to clients (0.3 ) (2.5 ) (26.1 ) Financial instruments sold, not yet purchased, at fair value 34.0 (10.6 ) 35.9 Net cash (used in) provided by operating activities (43.5 ) 35.5 (35.0 ) Cash flows from investing activities: Capital contribution in affiliates (4.5 ) — (48.4 ) Purchase of property and equipment (5.9 ) (6.1 ) (5.5 ) Net cash used in investing activities (10.4 ) (6.1 ) (53.9 ) Cash flows from financing activities: Net change in lenders under loans 58.2 13.5 108.5 Payments of notes payable (0.8 ) (0.8 ) (0.8 ) Repayment of senior unsecured notes — (45.5 ) — Deferred payments on acquisitions (5.5 ) — (2.9 ) Share repurchase — — (19.5 ) Debt issuance costs — — (1.9 ) Exercise of stock options 2.6 3.4 3.5 Withholding taxes on stock option exercises (0.8 ) — — Income tax benefit on stock options and awards — 0.7 0.8 Net cash provided by (used in) financing activities 53.7 (28.7 ) 87.7 Net (decrease) increase in cash and cash equivalents (0.2 ) 0.7 (1.2 ) Cash and cash equivalents at beginning of period 2.0 1.3 2.5 Cash and cash equivalents at end of period $ 1.8 $ 2.0 $ 1.3 Supplemental disclosure of cash flow information: Cash paid for interest $ 15.0 $ 8.2 $ 9.0 Income taxes (received) paid, net of cash refunds $ (18.4 ) $ (22.3 ) $ (33.8 ) Supplemental disclosure of non-cash investing and financing activities: Additional consideration payable related to acquisitions $ — $ (0.2 ) $ (0.4 )

Subsequent Events Subsequent Ev

Subsequent Events Subsequent Events (Notes)	12 Months Ended
	Sep. 30, 2018
Subsequent Events [Abstract]
Subsequent Events [Text Block]	Note 23 – Subsequent Events During the week ended November 16, 2018, balances in approximately 300 accounts of the FCM division of the Company’s wholly owned subsidiary, INTL FCStone Financial, declined below required maintenance margin levels, primarily as a result of significant price fluctuations in the natural gas markets. All positions in these accounts, which were managed by OptionSellers.com Inc. (“OptionSellers”), an independent Commodity Trading Advisor (“CTA”), were liquidated in accordance with the INTL FCStone Financial’s customer agreements and obligations under market regulation standards. A CTA is by definition registered with the CFTC and a member of, and subject to audit by, the NFA. OptionSellers is registered under a CFTC Rule 4.7 exemption for “qualified eligible persons”, which requires the account holders authorizing OptionSellers to act as their CTA to meet or exceed certain minimum financial requirements. OptionSellers, in its role as a CTA, had been granted by each of its customers full discretionary authority to manage the trading in the customer accounts, while INTL FCStone Financial acted solely as the clearing firm in its role as the FCM, at all times meeting its obligations as the FCM to these accounts. INTL FCStone Financial’s customer agreements conform to NFA guidance, disclose the risks to which account-holders are exposed, hold account-holders liable for all losses in their accounts, and obligate the account holders to reimburse INTL FCStone Financial for any account deficits in their accounts. INTL FCStone Financial continues to pursue collection of these receivables in the ordinary course of business. INTL FCStone Financial intends both to enforce and to defend its rights aggressively, and to claim interest and costs of collection where applicable. INTL FCStone Financial’s standard customer agreements provide for arbitration of disputes between parties. As of December 10, 2018, the aggregate receivable from these customer accounts, net of collections and other allowable deductions thus far, is $31.3 million , with no individual account receivable exceeding $1.4 million . The exposure to losses from these customer accounts is not yet determinable, as collection efforts are in early stages, given the timing of events that lead to the receivable balances disclosed above. Depending on future collections and an assessment to be made under U.S. GAAP, any provisions for bad debts and actual losses ultimately may or may not be material to the Company’s financial results. The Company believes that these accounts receivable balances, along with possible exposure to losses from these customer accounts, will not impact the Company’s ability to comply with its ongoing liquidity, capital, and regulatory requirements.

Description of Business and S_2

Description of Business and Significant Accounting Policies (Policies)	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Accounting Policies [Abstract]
Basis of Presentation, Policy [Policy Text Block]	Basis of Presentation The accompanying consolidated financial statements include the accounts of INTL FCStone Inc. and all other entities in which the Company has a controlling financial interest. All material intercompany transactions and balances have been eliminated in consolidation. Unless otherwise stated herein, all references to fiscal 2018 , fiscal 2017 , and fiscal 2016 refer to the Company’s fiscal years ended September 30. In the consolidated income statements, the total revenues reported combine gross revenues for the physical commodities business and net revenues for all other businesses. The subtotal ‘operating revenues’ in the consolidated income statements is calculated by deducting physical commodities cost of sales from total revenues. The subtotal ‘net operating revenues’ in the consolidated income statements is calculated as operating revenues less transaction-based clearing expenses, introducing broker commissions and interest expense. Transaction-based clearing expenses represent variable expenses paid to executing brokers, exchanges, clearing organizations and banks in relation to transactional volumes. Introducing broker commissions include commission paid to non-employee third parties that have introduced clients to the Company. Net operating revenues represent revenues available to pay variable compensation to risk management consultants and traders and direct non-variable expenses, as well as variable and non-variable expenses of operational and administrative employees.
Consolidation, Policy [Policy Text Block]	The accompanying consolidated financial statements include the accounts of INTL FCStone Inc. and all other entities in which the Company has a controlling financial interest. All material intercompany transactions and balances have been eliminated in consolidation.
Fiscal Period, Policy [Policy Text Block]		Unless otherwise stated herein, all references to fiscal 2018 , fiscal 2017 , and fiscal 2016 refer to the Company’s fiscal years ended September 30.
Use of Estimates, Policy [Policy Text Block]	Use of Estimates The preparation of consolidated financial statements in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”) requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent liabilities as of the date of the financial statements and the reported amounts of revenue and expenses during the reporting period. The most significant of these estimates and assumptions relate to fair value measurements for financial instruments, revenue recognition, the provision for probable losses from bad debts, valuation of inventories, valuation of goodwill and intangible assets, and incomes taxes and contingencies. These estimates are based on management’s best knowledge of current events and actions the Company may undertake in the future. The Company reviews all significant estimates affecting the financial statements on a recurring basis and records the effect of any necessary adjustments prior to their issuance. Although these and other estimates and assumptions are based on the best available information, actual results could be materially different from these estimates.
Foreign Currency Translations Policy [Policy Text Block]	Foreign Currency Translation
Cash and Cash Equivalents, Unrestricted Cash and Cash Equivalents, Policy [Policy Text Block]	Cash and Cash Equivalents The Company considers cash held at banks and all highly liquid investments not held for trading purposes, with original or acquired maturities of 90 days or less, including certificates of deposit, to be cash and cash equivalents. Cash and cash equivalents consist of cash, foreign currency, and certificates of deposit not deposited with or pledged to exchange-clearing organizations, broker-dealers, clearing organizations or counterparties, or segregated under federal or other regulations. Certificates of deposit are stated at cost plus accrued interest, which approximates fair value
Cash, Securities and Other Assets Segregated, Restricted Cash and Cash Equivalents, Policy [Policy Text Block]	Cash, Securities and Other Assets Segregated under Federal and other Regulations Pursuant to requirements of the Commodity Exchange Act and Commission Regulation 30.7 of the U.S. Commodity Futures Trading Commission (“CFTC”) in the U.S. and similarly in the United Kingdom (“U.K.”), pursuant to the Markets in Financial Instruments Implementing Directive 2006/73/EC underpinning the Client Asset (“CASS”) rules in the Financial Services Authority (“FSA”) handbook, funds deposited by clients relating to futures and options on futures contracts in regulated commodities must be carried in separate accounts which are designated as segregated client accounts. Additionally, in accordance with Rule 15c3-3 of the Securities Exchange Act of 1934 (“Rule 15c3-3”), the Company maintains separate accounts for the exclusive benefit of securities clients and proprietary accounts of broker dealers (“PABs”). Rule 15c3-3 requires the Company to maintain special reserve bank accounts (“SRBAs”) for the exclusive benefit of securities clients and PABs. The deposits in segregated client accounts and SRBAs are not commingled with the funds of the Company. Under the FSA’s rules, certain categories of clients may choose to opt-out of segregation. As of September 30, 2018 and 2017 , cash, securities, and other assets segregated under federal and other regulations consisted of cash held at banks of approximately $765.4 million and $464.3 million , respectively, U.S. Treasury obligations of approximately $600.4 million and $33.5 million , respectively, and commodities warehouse receipts of approximately $42.9 million and $21.0 million , respectively (see fair value measurements discussion in Note 3 ).
Commodity Repurchase and Other Repurchase Agreements Policy [Policy Text Block]	Securities Purchased/Sold Under Agreements to Resell/Repurchase The Company enters into securities purchased under agreements to resell (reverse repurchase agreements) and securities sold under agreements to repurchase (repurchase agreements) primarily to finance financial instruments, acquire securities to cover short positions or to acquire securities for settlement. Reverse repurchase agreements and repurchase agreements are treated as collateralized financing transactions and are recorded at their contractual amounts plus accrued interest. The related interest is recorded in the 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, or may be required by 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.
Securities Borrowed and Loaned Policy [Policy Text Block]	Securities Borrowed and Loaned The Company enters into securities borrowed and securities loaned transactions primarily to meet counterparties’ needs. Securities borrowed and securities loaned are reported as collateralized financings. Securities borrowed and securities loaned transactions are recorded at the amount of cash collateral advanced or received. The Company receives collateral generally in excess of the market value of securities loaned. The Company monitors the market value of securities borrowed and loaned on a daily basis, with additional collateral obtained or refunded as necessary. Securities borrowed and securities loaned are reported on a gross basis. Interest income and interest expense are recognized over the life of the arrangements.
Deposits and Receivables from Exchange-Clearing Organizations, Broker-dealers, Clearing Organizations and Counterparties, and Payables to Broker-dealers, Clearing Organizations and Counterparties Disclosure [Text Block]	Deposits with and Receivables from Broker-dealers, Clearing Organizations and Counterparties, and Payables to Broker-dealers, Clearing Organizations and Counterparties As required by the regulations of the CFTC and the aforementioned FSA handbook, client funds received to margin, guarantee, and/or secure commodity futures and futures on options transactions are segregated and accounted for separately from the general assets of the Company. Deposits with broker-dealers, clearing organizations, and counterparties pertain primarily to deposits made to satisfy margin requirements on client and proprietary open futures and options on futures positions and to satisfy the requirements set by clearing exchanges for clearing membership. The Company also pledges margin deposits with various counterparties for OTC derivative contracts, and these deposits are also included in deposits with broker-dealers, clearing organizations, and counterparties. The Company also deposits cash margin with various securities clearing organizations, and these deposits are also included in deposits with broker-dealers, clearing organizations, and counterparties. Deposits with and receivables from broker-dealers, clearing organizations, and counterparties are reported gross, except where a right of offset exists. As of September 30, 2018 and 2017 , the Company had cash and cash equivalents on deposit with or pledged to broker-dealers, clearing organizations, and counterparties of approximately $1.5 billion and $2.3 billion , respectively. Deposits with and receivables from broker-dealers, clearing organizations, and counterparties also include securities pledged to exchange-clearing organizations as collateral in lieu of cash margin by the Company on behalf of clients and client-owned securities that are pledged directly. It is the Company’s practice to include client-owned securities on its consolidated balance sheets, as the rights to those securities have been transferred to the Company under the terms of the futures trading agreements. Securities pledged primarily include U.S. Treasury obligations, foreign government obligations, and certain exchange-traded funds (“ETFs”). Securities that are not client-owned are adjusted to fair value with associated changes in unrealized gains or losses recorded through current period earnings. For client-owned securities, the change in fair value is offset against the payable to clients with no impact recognized in the consolidated income statements. The fair value of these securities included within deposits with and receivables from broker-dealers, clearing organizations, and counterparties was $785.8 million and $251.4 million as of September 30, 2018 and 2017 , respectively. Management has considered guidance required by Accounting Standards Codification (“ASC”) 860 - Transfers and Servicing as it relates to securities pledged by clients to margin their accounts within the FCM Division of INTL FCStone Financial. Based on a review of the agreements with the client, management believes the transferor surrenders control over those assets because: (a) the transferred assets have been isolated from the transferor—put presumptively beyond the reach of the transferor and its creditors, even in bankruptcy or other receivership, (b) each transferee has the right to pledge or exchange the assets (or beneficial interests) it received, and no condition both constrains the transferee (or holder) from taking advantage of its right to pledge or exchange and provides more than a trivial benefit to the transferor and (c) the transferor does not maintain effective control over the transferred assets through either (1) an agreement that both entitles and obligates the transferor to repurchase or redeem them before their maturity or (2) the ability to unilaterally cause the holder to return specific assets, other than through a cleanup call. Under this guidance, the Company reflects the client collateral assets and corresponding liabilities in the Company’s consolidated balance sheets as of September 30, 2018 and 2017 . In addition to cash margin, deposits with and receivables from broker-dealers, clearing organizations, and counterparties include guaranty deposits with exchange-clearing organizations. The guaranty deposits are held by the clearing organization for use in potential default situations by one or more members of the clearing organization. The guaranty deposits may be applied to the Company’s obligations to the clearing organization, or to the clearing organization’s obligations to other clearing members or third parties. The Company maintains client omnibus and proprietary accounts with other counterparties, and the equity balances in those accounts along with any margin cash or securities deposited with the carrying broker are included in deposits with and receivables from broker-dealers, clearing organizations, and counterparties. Deposits with and receivables from broker-dealers, clearing organizations, and counterparties also include amounts due from or due to exchange-clearing organizations for daily variation settlements on open futures and options on futures positions. The variation settlements due from or due to exchange-clearing organizations are paid in cash on the following business day and represent the settlement of futures positions. Deposits with and receivables from broker-dealers, clearing organizations and counterparties, and payables to broker-dealers, clearing organizations and counterparties also include amounts related to the value of clients cross-currency payment transactions related to the Global Payments segment. These amounts arise due to a clearing period before the funds are received and payments are made, which usually is one to two business days. Deposits with and receivables from broker-dealers, clearing organizations, and counterparties also includes amounts due from exchange-clearing organizations for unrealized gains and losses associated with clients’ options on futures contracts. See discussion in the Financial Instruments section below for additional information on the Company’s accounting policies for derivative contracts. For client-owned derivative contracts, the fair value is offset against the payable to clients with no impact recognized on the consolidated income statements.
Receivable from and Payable to Customers, Policy [Policy Text Block]	Receivable from and Payable to Clients Receivable from clients, net of the allowance for doubtful accounts, include the total of net deficits in individual exchange-traded futures and OTC derivative trading accounts carried by the Company. Client deficits arise from realized and unrealized trading losses on client futures, options on futures, swaps and forwards and amounts due on cash and margin transactions. Client deficit accounts are reported gross of client accounts that contain net credit or positive balances, except where a right of offset exists. Net deficits in individual futures exchange-traded and OTC derivative trading accounts include both secured and unsecured deficit balances due from clients as of the balance sheet date. Secured deficit amounts are backed by U.S. Treasury obligations and commodity warehouse receipts. These U.S Treasury obligations and commodity warehouse receipts are not netted against the secured deficit amounts, as the conditions for right of setoff have not been met. Receivable from clients, net also includes the net amounts receivable from securities clients in connection with the settlement of regular-way cash securities, margin loans to clients, and client cash debits. It is the Company’s policy to report margin loans and payables that arise due to positive cash flows in the same client’s accounts on a net basis when the conditions for netting as specified in U.S. GAAP are met. Clients’ securities transactions cleared by the Company are recorded on a settlement date basis. Securities cleared by the Company and pledged to the Company as a condition of the custodial clearing arrangements are owned by the clients, including those that collateralize margin or other similar transactions, and are not reflected on the consolidated balance sheets as the Company does not have title to, or beneficial interests, in those assets. In the event of uncompleted transactions on settlement date, the Company records corresponding receivables and payables, respectively. The carrying value of the receivables and payables approximates fair value due to their short-term nature. Payable to clients represent the total of client accounts with credit or positive balances. Client accounts are used primarily in connection with commodity, foreign exchange, precious metals, and securities transactions and include gains and losses on open trades as well as securities and cash margin deposits made as required by the Company, the exchange-clearing organizations or other clearing organizations. Client accounts with credit or positive balances are reported gross of client deficit accounts, except where a right of offset exists. Receivable from and payables to clients also include amounts related to the value of clients cross-currency payment transactions related to the Global Payments segment. These amounts arise due to a clearing period before the funds are received and payments are made, which usually is one to two business days. The future collectability of receivables from clients can be impacted by the Company’s collection efforts, the financial stability of its clients, and the general economic climate in which it operates. The Company evaluates accounts that it believes may become uncollectible on a specific identification basis, through reviewing daily margin deficit reports, the historical daily aging of the receivables, and by monitoring the financial strength of its clients. The Company may unilaterally close client trading positions in certain circumstances. In addition, to evaluate client margining and collateral requirements, client positions are stress tested regularly and monitored for excessive concentration levels relative to the overall market size. Furthermore, in certain instances, the Company is indemnified, and able to charge back, introducing broker-dealers for bad debts incurred by their clients. The Company generally charges off an outstanding receivable balance when all economic means of recovery have been exhausted. That determination considers information such as the occurrence of significant changes in the client’s financial position such that the client can no longer pay the obligation, or that the proceeds from collateral will not be sufficient to pay the balance.
Notes Receivable, Policy [Policy Text Block]	Notes Receivable Accrual of commodity financing income on any note is discontinued when, in the opinion of management, there is reasonable doubt as to the timely collectability of interest or principal. Nonaccrual notes are returned to an accrual status when, in the opinion of management, the financial position of the borrower indicates there is no longer any reasonable doubt as to the timely payment of principal and interest. The Company records a charge against earnings for notes receivable losses when management believes that the collection of outstanding principal is not probable.
Physcial Commodities Inventory, Policy [Policy Text Block]	Physical Commodities Inventory Inventories of certain agricultural commodities are carried at net realizable value, which approximates fair value less disposal costs. The agricultural commodities inventories have reliable, readily determinable and realizable market prices, have relatively predictable and insignificant costs of disposal and are available for immediate delivery. Changes in the fair values of these agricultural commodities inventories are included as a component of ‘cost of physical commodities sold’ in the consolidated income statements. Inventories of energy related products are valued at the lower of cost or net realizable value. Inventories of precious metals held by subsidiaries that are not broker-dealers are valued at the lower of cost or net realizable value, using the weighted-average price and first-in first-out costing method. Precious metals inventory held by INTL FCStone Ltd, a U.K. based broker-dealer subsidiary, is measured at fair value, with changes in fair value included as a component of ‘trading gains, net’ in the consolidated income statements.
Property and Equipment, Policy [Policy Text Block]	Property and Equipment Property and equipment is stated at cost, net of accumulated depreciation and amortization and depreciated using the straight-line method over the estimated useful lives of the assets. Leasehold improvements are amortized on a straight-line basis over the estimated useful life of the improvement or the term of the lease, whichever is shorter. Certain costs of software developed or obtained for internal use are capitalized and amortized over the estimated useful life of the software. Expenditures for maintenance, repairs, and minor replacements are charged against earnings, as incurred. Expenditures that increase the value or productive capacity of assets are capitalized. When property and equipment are retired, sold, or otherwise disposed of, the asset’s carrying amount and related accumulated depreciation are removed from the accounts and any gain or loss is included in earnings.
Goodwill and Intangible Assets, Policy [Policy Text Block]	Goodwill and Identifiable Intangible Assets Goodwill is the cost of acquired companies in excess of the fair value of identifiable net assets at the acquisition date. Goodwill is not subject to amortization, but rather is evaluated for impairment at least annually. The Company evaluates its goodwill for impairment at the fiscal year end (or more frequently if indicators of potential impairment exist) in accordance with ASC 350 - Intangibles - Goodwill and Other . Goodwill impairment is determined by comparing the estimated fair value of a reporting unit with its respective carrying value. If the estimated fair value exceeds the carrying value, goodwill at the reporting unit level is not deemed to be impaired. However, if the estimated fair value is below carrying value, further analysis is required to determine the amount of the impairment. This further analysis involves assigning tangible assets and liabilities, identified intangible assets and goodwill to reporting units and comparing the fair value of each reporting unit to its carrying amount. In the course of the evaluation of the potential impairment of goodwill, the Company may perform either a qualitative or a quantitative assessment. The Company’s qualitative assessment of potential impairment may result in the determination that a quantitative impairment analysis is not necessary. Under this elective process, the Company assesses qualitative factors to determine whether the existence of events or circumstances leads the Company to determine that it is more likely than not that the fair value of a reporting unit is less than its carrying amount. If after assessing the totality of events or circumstances, the Company determines it is more likely than not that the fair value of a reporting unit is greater than its carrying amount, then performing a quantitative analysis is not required. However, if the Company concludes otherwise, then the Company performs a quantitative impairment analysis. If the Company either chooses not to perform a qualitative assessment, or the Company chooses to perform a qualitative assessment but is unable to qualitatively conclude that no impairment has occurred, then the Company performs a quantitative evaluation. In the case of a quantitative assessment, the Company estimates the fair value of the reporting unit which the goodwill that is subject to the quantitative analysis is associated (generally defined as the businesses for which financial information is available and reviewed regularly by management) and compares it to the carrying value. If the estimated fair value of a reporting unit is less than its carrying value, the Company estimates the fair value of all assets and liabilities of the reporting unit, including goodwill. If the carrying value of the reporting unit’s goodwill is greater than the estimated fair value, an impairment charge is recognized for the excess. The fair value of the Company’s reporting units exceeded their respective carrying values under the first step of the quantitative assessment and no impairment charges were recorded for any of the periods presented. Identifiable intangible assets subject to amortization are amortized using the straight-line method over their estimated period of benefit, ranging from two to twenty years. Identifiable intangible assets are tested for impairment whenever events or changes in circumstances suggest that an asset’s or asset group’s carrying value may not be fully recoverable. Residual value is presumed to be zero for all identifiable intangible assets.
Financial Instruments and Derivatives, Policy [Policy Text Block]	Financial Instruments Owned and Sold, Not Yet Purchased Financial instruments owned and sold, not yet purchased, at fair value consist of financial instruments carried at fair value on a recurring basis or amounts that approximate fair value, with related realized and unrealized gains and losses recognized in current period earnings. Realized and unrealized gains and losses on financial instruments owned and sold, not yet purchased, are included in ‘Trading gains, net’ and ‘Cost of sales of physical commodities’ in the consolidated income statements. The fair value of a financial instrument is the amount at which the instrument could be exchanged in a current transaction between willing parties, other than in a forced or liquidation sale. Financial instruments owned and sold, not yet purchased are comprised primarily of the financial instruments held by the Company’s broker-dealer subsidiaries and the Company’s over-the-counter (“OTC”) derivative swap dealer. Financial instruments owned and financial instruments sold, not yet purchased, includes trading securities that the Company holds as a principal. The Company has not classified any financial instruments owned or sold, not yet purchased, as available-for-sale or held-to-maturity. Financial instruments owned and sold, not yet purchased includes derivative instruments that the Company holds as a principal which are primarily transacted on an OTC basis. As a derivatives dealer, the Company utilizes derivative instruments to manage exposures to foreign currency, commodity price and interest rate risks for the Company and its clients. The Company’s objectives for holding derivatives include reducing, eliminating, and efficiently managing the economic impact of these exposures as effectively as possible. The Company’s derivative instruments also include forward purchase and sale commitments for the physical delivery of agricultural and energy related commodities in a future period. Contracts to purchase agricultural and energy commodities generally relate to the current or future crop year. Contracts for the sale of agricultural and energy commodities generally do not extend beyond one year. Derivative instruments are recognized as either assets or liabilities and are measured at fair value on a recurring basis. As the Company does not elect hedge accounting for any derivative instruments, realized and unrealized gains and losses from the change in fair value of derivative instruments are recognized immediately in current period earnings. Realized and unrealized gains and losses from the derivative instruments in which the Company acts as a dealer are included within ‘Trading gains, net’ on the consolidated income statements. Realized and unrealized gains and losses on firm purchase and sale commitments are included within ‘Cost of sales of physical commodities’ on the consolidated income statements. To reduce credit exposure on the derivative instruments for which the Company acts as a dealer, the Company may enter into a master netting arrangement that allows for settlement of all derivative transactions with each counterparty. In addition, the credit support annex that accompanies master netting arrangements allows parties to the master netting agreement to mitigate their credit risk by requiring the party which is out of the money to post collateral. The Company accepts collateral in the form of cash or other marketable securities. Where permitted, the Company elects to net-by-counterparty certain derivative instruments entered into under a legally enforceable master netting agreement and, therefore, the fair value of those derivative instruments are netted by counterparty in the consolidated balance sheets. As the Company elects to net-by-counterparty the fair value of such derivative instruments, the Company also nets-by-counterparty cash collateral exchanged as part of those derivative instruments. The Company also brokers foreign exchange forwards, options and cash, or spot, transactions between clients and external counterparties. A portion of the contracts are arranged on an offsetting basis, limiting the Company’s risk to performance of the two offsetting parties. The offsetting nature of the contracts eliminates the effects of market fluctuations on the Company’s operating results. Due to the Company’s role as a principal participating in both sides of these contracts, the amounts are presented gross on the consolidated balance sheets at their respective fair values, net of offsetting assets and liabilities. The Company holds proprietary positions in its foreign exchange line of business. On a limited basis, the Company’s foreign exchange trade desk will accept a client transaction and will offset that transaction with a similar but not identical position with a counterparty. These unmatched transactions are intended to be short-term in nature and are often conducted to facilitate the most effective transaction for the Company’s client. These spot and forward contracts are accounted for as free-standing derivatives and reported in the consolidated balance sheets at their fair values. The Company may lease commodities to or from clients or counterparties. These commodity leases, which primarily involve precious metals, are recorded at fair value utilizing the fair value option based on guidance in the Financial Instruments Topic of the ASC. These commodities leases represent hybrid financial instruments which contain both a dollar denominated loan host contract and an embedded forward derivative contract on the underlying commodities, which can be settled in either cash or metals. As permitted by the fair value option election, the entire instrument is recorded at fair value as either an asset or liability in the consolidated balance sheets. The corresponding change in the fair value of the instrument is recognized in the consolidated income statements as a component of ‘trading gains, net’ for the fiscal years ended September 30, 2018, 2017, and 2016 . The Company does elect to value all of their commodities lease agreements at fair value using the fair value option.
Exchange Memberships and Stock, Policy [Policy Text Block]	Exchange and Clearing Organization Memberships and Stock The Company is required to hold certain exchange membership seats and exchange firm and clearing organization common stock and pledges them for clearing purposes, in order to provide the Company the right to process trades directly with the various exchanges and clearing organizations. Exchange memberships include seats on the Chicago Board of Trade (“CBOT”), the Minneapolis Grain Exchange, the New York Mercantile Exchange (“NYMEX”), the Commodity Exchange, Inc. (“COMEX”) Division of the New York Mercantile Exchange, Mercado de Valores de Buenos Aires S.A. (“MERVAL”), the Chicago Mercantile Exchange (“CME”) Growth and Emerging Markets, InterContinental Exchange, Inc. (“ICE”) Futures US, ICE Europe Ltd and London Metal Exchange (“LME”). Exchange firm and clearing organization common stock include shares of CME Group, Inc., ICE, LME, and the Depository Trust & Clearing Corporation (“DTCC”). Exchange and clearing organization memberships and firm common stocks required in order to conduct business on exchanges and clearing organizations are recorded at cost and are included in ‘other assets’ on the consolidated balance sheets. Equity investments in exchange firm common stock not required in order to conduct business on the exchanges are classified as trading securities included within ‘financial instruments owned’ on the consolidated balance sheets and recorded at fair value, with unrealized gains and losses recorded as a component of ‘trading gains, net’ on the consolidated income statements. The cost basis for exchange and clearing organization memberships and firm common stock pledged for clearing purposes was $11.4 million and $12.0 million as of September 30, 2018 and 2017 , respectively. The fair value of exchange and clearing organization memberships and firm common stock pledged for clearing purposes was $10.3 million and $10.2 million as of September 30, 2018 and 2017 , respectively. The fair value of exchange and clearing organization firm common stock is determined by quoted market prices, and the fair value of exchange memberships is determined by recent sale transactions. The Company monitors the fair value of exchange and clearing organization membership seats and firm common stock on a quarterly basis, and does not consider any current unrealized losses on individual exchange and clearing organization memberships and firm common stock to be anything other than a temporary impairment.
Debt, Policy [Policy Text Block]	Lenders Under Loans Lenders under loans are accounted for at amortized cost
Business Combinations and Contingent Consideration Policy [Policy Text Block]	When acquiring companies, the Company recognizes separately from goodwill most of the identifiable assets acquired and the liabilities assumed at their acquisition date fair values. Certain contingent liabilities acquired require remeasurement at fair value in each subsequent reporting period. Goodwill as of the acquisition date is measured as the excess of consideration transferred and the net of the acquisition fair values of the assets acquired and liabilities assumed. While the Company used its best estimates and assumptions as a part of the purchase price allocation to accurately value assets acquired and liabilities assumed at the acquisition date, these estimates are inherently uncertain and subject to refinement. As a result, during the remeasurement period, which may up to one year from the acquisition date, the Company records adjustments to the assets acquired and liabilities assumed, with the corresponding offset to goodwill. Upon conclusion of the measurement period or final determination of the values of assets acquired and liabilities assumed, whichever comes first, any subsequent adjustments are recorded to the consolidated income statements rather than adjusted through goodwill. Acquisition related costs, such as fees for attorneys, accountants, and investment bankers, are expensed as incurred and are not capitalized as part of the purchase price. Determining the fair value of certain identifiable assets acquired and liabilities assumed is subjective in nature and often involves the use of significant estimates and assumptions. Estimating the fair value of the assets and liabilities acquired requires significant judgment. These estimates and assumptions are based in part on historical experience, market data, and information obtained from the management of the acquired companies. Among the significant estimates used to value certain identifiable intangible assets acquired in acquisitions include, but are not limited to future expected cash flows from customer relationships and discount rates. Contingent Consideration The Company estimates and records the acquisition date estimated fair value of contingent consideration as part of purchase price consideration for acquisitions. Additionally, each reporting period, the Company estimates changes in the fair value of contingent consideration, and any change in fair value is recognized in the consolidated income statements. An increase in the contingent consideration expected to be paid will result in a charge to operations in the period that the anticipated fair value of contingent consideration increases, while a decrease in the earn-out expected to be paid will result in a credit to operations in the period that the anticipated fair value of contingent consideration decreases. The estimate of the fair value of contingent consideration requires subjective assumptions to be made of future operating results, discount rates, and probabilities assigned to various potential operating result scenarios.
Additional Paid-In Capital, Policy [Policy Text Block]	Additional Paid-In Capital The Company’s additional paid-in capital (“APIC”) consists of stockholder contributions that are in excess of par value of common stock. Included in APIC are amounts related to the exercise of stock options and amortization of share-based compensation
Revenue Recognition, Policy [Policy Text Block]	Revenue Recognition Sales of physical commodities Sales of physical commodities revenue are recognized when persuasive evidence of an arrangement exists, delivery has occurred, the fee is fixed or determinable, and collectability is reasonably assured. The Company reports its physical commodities revenues, except as described below, on a gross basis, with the corresponding cost of sales shown separately, in accordance with the guidelines provided in the Revenue Recognition Topic of the ASC. Management has historically assessed the performance of the physical commodities businesses on an operating revenue basis, and continues to do so. INTL FCStone Ltd precious metals sales and cost of sales are presented on a net basis and included as a component of ‘trading gains, net’ in the consolidated income statements, in accordance with U.S GAAP accounting requirements for broker-dealers. Precious metals sales and cost of sales for subsidiaries that are not broker-dealers continue to be recorded on a gross basis. Trading gains, net Trading gains, net include brokerage fees and margins generated from OTC derivative trades executed with clients and other counterparties and are recognized when trades are executed. Trading gains, net also include activities where the Company acts as principal in the purchase and sale of individual securities, currencies, commodities or derivative instruments. These transactions may be offset simultaneously with another client or counterparty, offset with similar but not identical positions on an exchange, made from inventory, or may be aggregated with other purchases to provide liquidity intraday, for a number of days, or in some cases even longer periods (during which fair value may fluctuate). In addition, trading gains, net includes activities from the Company’s operations of a proprietary foreign exchange desk which arbitrages the futures and cash markets (see additional discussion in the Financial Instruments Owned and Sold, Not Yet Purchased policy note for revenue recognition on principal trading activities). Net dealer inventory and investment gains are recognized on a trade-date basis and include realized gains or losses and changes in unrealized gains or losses on investments at fair value. Dividend income on long equity positions and dividend expense on short equity positions are recognized net in ‘trading gains, net’ on the ex-dividend date. Commission and clearing fees The Company generates two types of commission revenues: sales-based commissions and trailing commissions. Sales-based commission revenues, which occur when the Company executes and clears securities, futures, and options on futures transactions on behalf of clients in an agency capacity, primarily represent commissions that are recognized on a trade-date basis. Sales-based commissions are generated by internal traders and brokers or by introducing broker-dealers. Sales-based commissions are reported gross of introducing-broker dealer and registered investment advisor commissions. Certain commissions on futures contracts are recognized on a half-turn basis in two equal parts. The first half is recognized when the contract is opened and the second half is recognized when the transaction is closed. Commissions on options on futures contracts are generally recognized on a half-turn basis, except that full commissions are recognized on options expected to expire without being exercised or offset. Commissions and transactions fees are charged at various rates based on the type of account, the products traded, and the method of trade. Clearing and transaction fees are charged to clients on a per contract basis based on the trade-date. These fees are for clearing clients’ trades and include fees charged to the Company by the various futures exchanges, securities clearing organizations, and other regulatory organizations and are reported gross of the transaction-based clearing expenses discussed below. Trailing commission revenues from mutual funds, annuities, and insurance products are recorded over the period earned. Trailing commission revenues, or commissions that are paid over time, such as 12(b)-1 fees are recurring in nature and are earned based on varying factors that are product specific to trail-eligible assets. The Company earns trailing commission revenues primarily on mutual funds, annuities, and insurance products held by clients of the Company’s registered investment advisors. Consulting, management, and account fees Consulting, management, and account fees include risk management consulting fees which are billed and recognized as revenue on a monthly basis when risk management services are provided. Such agreements are generally for one year periods, but are generally cancelable by either party upon providing thirty days written notice to the other party and the amounts are not variable based on client trading activities. Fee income for structuring and arrangement of debt transactions and management and investment advisory income is recorded when the services related to the underlying transactions are provided and success fees are recorded when complete, as determined under the terms of the assignment or engagement. Consulting, management, and account fees also includes various charges related to securities clearing agreements with unaffiliated introducing-broker dealers such as transaction fees, annual account fees, service charges, servicing fees, platform fees, money market processing and distribution fees, and other correspondent clearing fees. The annual account fees such as IRA fees and distribution fees are recognized as earned over the term of the contract. The transaction fees are earned and collected from clients as trades are executed. Servicing fees such as omnibus fees are paid to the Company for marketing and administrative services and are recognized as earned. Consulting, management, and account fees also includes fund management fees which are earned over the period in which services are rendered. The fund management fees earned are calculated monthly based upon an average of net assets under management in accordance with such investment management agreements. Consulting, management, and account fees also includes asset management, or administration, fees generated from the Company’s registered investment advisor platform based upon the value of their advisory assets. Asset management, or administration, fees are generally billed to clients at the beginning of the quarter and are recognized as revenue ratably over the quarter. The majority of accounts are billed in advance using values as of the last business day of each calendar quarter. The market value of the assets in an account on the billing date determines the amount billed, and accordingly, the revenues earned in the following three month period. Additionally, the Company earns fees generated in lieu of interest income from a multi-bank sweep program with unaffiliated banks. Pursuant to contractual arrangements with securities introducing-broker dealers, uninvested cash balances in the introducing -brokers client accounts are swept into either FDIC insured cash accounts at various banks or third-party money market funds for which the Company earns a portion of the interest income generated by the balances. The fees generated by the Company’s multi-bank sweep program are reported net of the balances remitted to the introducing-brokers and the clients of introducing-brokers. Interest Income Interest income is recognized on an accrual basis. Interest income is generated from client funds deposited with the Company to satisfy margin requirements which is held by banks or pledged to exchange-clearing organizations. Interest income is also generated from the investment of client funds in U.S. Treasury obligations. Interest income generated from client funds is reported gross of the interest remitted to the clients. Interest is also generated from trading fixed income securities that the Company holds in its market-making businesses. Interest income also includes interest generated from collateralized transactions, including securities borrowed and securities purchased under agreements to resell, and from extending margin loans to clients. Revenue generally is recognized net of any taxes collected from clients and subsequently remitted to governmental authorities.
Cost of of Sales Physical Commodities, Policy [Policy Text Block]	Cost of Sales of Physical Commodities Cost of sales of physical commodities include finished commodity or raw material and processing costs along with operating costs relating to the receipt, storage and delivery of the physical commodities. Cost of sales of physical commodities also includes changes in the fair value of agricultural commodity inventories held for sale, and related forward purchase and sale commitments and exchange-traded futures and options contracts.
Interest Expense, Policy [Policy Text Block]	Interest Expense Interest expense is recognized on an accrual basis. As noted above, interest income is generated from client funds deposited with the Company to satisfy margin requirements which is held by banks or pledged to exchange-clearing organizations. Interest income is also generated from the investment of client funds in U.S. Treasury obligations. A portion of the interest income generated from these funds is remitted to the clients. Interest expense is also incurred on outstanding balances on the Company’s credit facilities. Interest expense is also incurred on fixed income securities sold, not yet purchased, that the Company holds in its market-marking businesses. Interest expense is also incurred from collateralized transactions, including securities loaned and securities sold under agreements to repurchase
Compensation and Benefits, Policy [Policy Text Block]	Compensation and Benefits Compensation and benefits consists primarily of salaries, incentive compensation, variable compensation, including commissions, related payroll taxes and employee benefits. The Company classifies employees as either risk management consultants / traders, operational or administrative personnel, which includes the executive officers. Variable compensation paid to risk management consultants and traders generally represents a fixed percentage of revenues generated, and in some cases, revenues produced less direct costs and an overhead allocation. The Company accrues commission expense on a trade-date basis.
Share-based Compensation Policy [Policy Text Block]	Share-Based Compensation The Company accounts for share-based compensation in accordance with the guidance of the Compensation-Stock Compensation Topic of the ASC. The cost of employee services received in exchange for a share-based award is generally measured based on the grant-date fair value of the award. Share-based employee awards that require future service are amortized over the relevant service period. Forfeitures are accounted for as they occur in determining share-based employee compensation expense. For option awards granted, compensation cost is recognized on a straight-line basis over the vesting period for the entire award.
Transaction-Based Clearing Expenses, Policy [Policy Text Block]	Transaction-Based Clearing Expenses Clearing fees and related expenses include primarily variable expenses for clearing and settlement services, including fees the Company pays to executing brokers, exchanges, clearing organizations and banks. These fees are based on transaction volume, and recorded as expense on the trade date. Clearing fees are passed on to clients and are presented gross in the consolidated statements of income under the Revenue Recognition Topic of the ASC, as the Company acts as a principal for these transactions.
Introducing Broker Commissions, Policy [Policy Text Block]	Introducing Broker Commissions Introducing broker commissions include commissions paid to non-employee third parties that have introduced clients to the Company. Introducing brokers are individuals or organizations that maintain relationships with clients and accept futures and options orders from those clients. The Company directly provides all account, transaction and margining services to introducing brokers, including accepting money, securities and property from the clients. The commissions are determined and settled monthly.
Income Tax, Policy [Policy Text Block]	Income Taxes Income tax expense includes U.S. federal, state and local and foreign income taxes. Certain items of income and expense are not reported in tax returns and financial statements in the same year. The objectives of accounting for income taxes are to recognize the amount of taxes payable or refundable for the current year. The Company utilizes the asset and liability method to provide income taxes on all transactions recorded in the consolidated financial statements. This method requires that income taxes reflect the expected future tax consequences of temporary differences between the carrying amounts of assets or liabilities for book and tax purposes. Accordingly, a deferred tax asset or liability for each temporary difference is determined based on the tax rates that the Company expects to be in effect when the underlying items of income and expense are realized. Judgment is required in assessing the future tax consequences of events that have been recognized in the Company’s financial statements or tax returns, including the repatriation of undistributed earnings of foreign subsidiaries. In assessing the realizability of deferred tax assets, management considers whether it is more likely than not that some or all of the deferred tax assets will not be realized. The Company recognizes the tax benefit from an uncertain tax position only if it is more likely than not that the tax position will be sustained on examination by the taxing authority, based upon the technical merits of the position. The tax benefit recognized in the consolidated financial statements from such a position is measured based on the largest benefit that has a greater than 50% likelihood of being realized upon ultimate settlement. See Note 18 for further information on the Company’s income taxes.
Comprehensive Income, Policy [Policy Text Block]	Comprehensive Income Comprehensive income consists of net income and other gains and losses affecting stockholders’ equity that, under U.S. GAAP, are excluded from net income. Other comprehensive income (loss) includes net actuarial gains and losses from defined benefit pension plans and gains and losses on foreign currency translations.
Preferred Stock [Text Block]	Preferred Stock The Company is authorized to issue one million shares of preferred stock, par value of $0.01 per share, in one or more classes or series to be established by the Company’s board of directors. As of September 30, 2018 and 2017 , no preferred shares were outstanding and the Company’s board of directors had not yet established any class or series of shares.
Recent Accounting Pronouncements, Policy [Policy Text Block]	Accounting Standards Adopted In March 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2016-09, “Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting” (“ASU 2016-09”), which simplifies several aspects of the accounting for share-based payment transactions. Under ASU 2016-09, excess tax benefits and tax deficiencies are recognized as income tax expense or benefit in the income statement instead of additional paid in capital. ASU 2016-09 also provides entities with the option to elect an accounting policy to estimate forfeitures of share-based awards over the service period or account for forfeitures when they occur. Under ASU 2016-09, previously unrecognized excess tax benefits should be recognized using a modified retrospective transition. In addition, amendments requiring recognition of excess tax benefits and tax deficiencies in the income statement, as well as changes in the computation of weighted-average diluted shares outstanding, should be applied prospectively. ASU 2016-09 is effective for and was adopted by the Company in the first quarter of 2018 and the impact of the adoption resulted in the following: • During the year ended September 30, 2018, the Company recognized excess tax benefits from share-based compensation of $0.5 million within income tax expense on the consolidated income statement and within net income on the consolidated cash flow statement. Prior to adoption, the tax effect of share-based awards would have been recognized in additional paid-in-capital on the consolidated balance sheets and separately stated in the financing activities in the consolidated cash flow statements. The Company has elected to adopt this guidance prospectively. • The Company has elected to account for forfeitures of share-based awards as they occur. The Company elected to account for forfeitures as they occur using a modified retrospective transition method. The adoption of this guidance did not have a material impact on the consolidated financial statements. • The excess tax benefits from the assumed proceeds available to repurchase shares were excluded in the computation of diluted earnings per share for the year ended September 30, 2018. The Company has elected to adopt this guidance prospectively. • For the year ended September 30, 2018, the Company has classified as a financing activity in the consolidated cash flow statement $0.8 million of cash paid to taxing authorities for restricted stock shares withheld to satisfy statutory income tax withholding obligations. The retrospective application of this guidance had no impact on the consolidated cash flow statements for the years ended September 30, 2017 and 2016. In July 2015, the FASB issued ASU No. 2015-11, “Simplifying the Measurement of Inventory (Topic 330).” Under ASU 2015-11, inventory that is measured using the first-in, first-out (FIFO), specific identification, or average cost methods should be measured at the lower of cost or net realizable value. This ASU does not impact inventory measurement under the last-in, first-out (LIFO) or retail inventory methods. The Company adopted this ASU prospectively in the first quarter of 2018. The adoption of this ASU did not have a material impact on the consolidated financial statements. In August 2018, the FASB issued ASU 2018-13, “Fair Value Measurement (Topic 820): Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement”, which aims to improve the overall usefulness of disclosures to financial statement users and reduce unnecessary costs to companies when preparing fair value measurement disclosures. This ASU is effective for all entities for annual and interim periods in fiscal years beginning after December 15, 2019. Retrospective adoption is required except for changes in disclosures related to changes in unrealized gains and losses included in other comprehensive income for Level 3 instruments, the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements, and the narrative description of measurement uncertainty. Early adoption is permitted. An entity may early adopt eliminated or modified disclosure requirements and delay adoption of the additional disclosure requirements until their effective date. In the fourth quarter of fiscal year 2018, the Company early adopted the eliminated disclosure requirements related to the amount of and reasons for transfers between Level 1 and Level 2 of the fair value hierarchy, the timing of transfers between levels of the fair value hierarchy, and the valuation processes for Level 3 fair value measurements. The early adoption of the eliminated disclosure requirements did not have a material impact on the Company’s fair value measurement disclosures included within Note 3 .

Earnings per Share (Tables)

Earnings per Share (Tables)	12 Months Ended
	Sep. 30, 2018
Earnings Per Share [Abstract]
Schedule of Calculation of Numerator and Denominator in Earnings Per Share [Table Text Block]	The following is a reconciliation of the numerator and denominator of the diluted net income per share computations for the periods presented below. Year Ended September 30, (in millions, except share amounts) 2018 2017 2016 Numerator: Net income $ 55.5 $ 6.4 $ 54.7 Less: Allocation to participating securities (0.9 ) (0.1 ) (1.0 ) Net income allocated to common stockholders $ 54.6 $ 6.3 $ 53.7 Denominator: Weighted average number of: Common shares outstanding 18,549,011 18,395,987 18,410,561 Dilutive potential common shares outstanding: Share-based awards 385,819 291,367 214,811 Diluted shares outstanding 18,934,830 18,687,354 18,625,372

Assets and Liabilities, at Fa_2

Assets and Liabilities, at Fair Value (Tables)	12 Months Ended
	Sep. 30, 2018
Assets and Liabilities, at Fair Value [Abstract]
Fair Value, Assets Measured on Recurring Basis [Table Text Block]	The following tables set forth the Company’s financial and nonfinancial assets and liabilities accounted for at fair value, on a recurring basis, as of September 30, 2018 and September 30, 2017 by level in the fair value hierarchy. There were no assets or liabilities that were measured at fair value on a nonrecurring basis as of September 30, 2018 and 2017 . September 30, 2018 (in millions) Level 1 Level 2 Level 3 Netting (1) Total Assets: Certificates of deposit $ 3.8 $ — $ — $ — $ 3.8 Unrestricted cash equivalents - certificates of deposit 3.8 — — — 3.8 Commodities warehouse receipts 42.9 — — — 42.9 U.S. Treasury obligations 600.4 — — — 600.4 Securities and other assets segregated under federal and other regulations 643.3 — — — 643.3 U.S. Treasury obligations 778.4 — — — 778.4 “To be announced” (TBA) and forward settling securities — 5.0 — (2.1 ) 2.9 Foreign government obligations 7.7 — — — 7.7 Derivatives 7,495.9 19.6 — (7,787.1 ) (271.6 ) Deposits with and receivables from broker-dealers, clearing organizations and counterparties 8,282.0 24.6 — (7,789.2 ) 517.4 Equity securities 71.2 3.0 — — 74.2 Corporate and municipal bonds — 79.1 — — 79.1 U.S. Treasury obligations 120.1 — — — 120.1 U.S. government agency obligations — 472.9 — — 472.9 Foreign government obligations 6.4 — — — 6.4 Agency mortgage-backed obligations — 1,022.5 — — 1,022.5 Asset-backed obligations — 42.9 — — 42.9 Derivatives 0.8 514.6 — (329.3 ) 186.1 Commodities leases — 29.5 — (11.8 ) 17.7 Commodities warehouse receipts 16.4 — — — 16.4 Exchange firm common stock 10.2 — — — 10.2 Mutual funds and other 6.3 — — — 6.3 Financial instruments owned 231.4 2,164.5 — (341.1 ) 2,054.8 Physical commodities inventory 42.1 114.8 — — 156.9 Total assets at fair value $ 9,202.6 $ 2,303.9 $ — $ (8,130.3 ) $ 3,376.2 Liabilities: Accounts payable and other accrued liabilities - contingent liabilities $ — $ — $ — $ — $ — TBA and forward settling securities — 2.1 — (2.1 ) — Derivatives 7,809.3 11.6 — (7,820.9 ) — Payables to broker-dealers, clearing organizations and counterparties 7,809.3 13.7 — (7,823.0 ) — Equity securities 51.1 0.4 — — 51.5 Corporate and municipal bonds — 20.1 — — 20.1 U.S. Treasury obligations 484.8 — — — 484.8 U.S government agency obligations — 57.2 — — 57.2 Agency mortgage-backed obligations — 0.2 — — 0.2 Derivatives — 688.0 — (494.6 ) 193.4 Commodities leases — 75.5 — (16.2 ) 59.3 Financial instruments sold, not yet purchased 535.9 841.4 — (510.8 ) 866.5 Total liabilities at fair value $ 8,345.2 $ 855.1 $ — $ (8,333.8 ) $ 866.5 (1) Represents cash collateral and the impact of netting across the levels of the fair value hierarchy. Netting among positions classified within the same level are included in that level. September 30, 2017 (in millions) Level 1 Level 2 Level 3 Netting (1) Total Assets: Certificate of deposits $ 3.8 $ — $ — $ — $ 3.8 Unrestricted cash equivalents - certificates of deposits 3.8 — — — 3.8 Commodities warehouse receipts 21.0 — — — 21.0 U.S. Treasury obligations 33.5 — — — 33.5 Securities and other assets segregated under federal and other regulations 54.5 — — — 54.5 Foreign government obligations — 6.4 — — 6.4 U.S. Treasury obligations 244.7 — — — 244.7 TBA and forward settling securities — 8.8 — — 8.8 Derivatives 2,608.6 289.1 — (2,952.9 ) (55.2 ) Deposits and receivables from broker-dealers, clearing organizations and counterparties 2,853.3 304.3 — (2,952.9 ) 204.7 Equity securities 40.4 4.6 0.1 — 45.1 Corporate and municipal bonds 28.2 0.9 — — 29.1 U.S. Treasury obligations 60.0 — — — 60.0 U.S. government agency obligations — 368.9 — — 368.9 Foreign government obligations — 10.2 — — 10.2 Agency mortgage-backed obligations — 920.9 — — 920.9 Asset-backed obligations — 47.3 — — 47.3 Derivatives 1.3 1,413.4 — (1,252.6 ) 162.1 Commodities leases — 174.1 — (138.7 ) 35.4 Commodities warehouse receipts 38.5 — — — 38.5 Exchange firm common stock 8.3 — — — 8.3 Mutual funds and other 6.0 — — — 6.0 Financial instruments owned 182.7 2,940.3 0.1 (1,391.3 ) 1,731.8 Physical commodities inventory 73.2 — — — 73.2 Total assets at fair value $ 3,167.5 $ 3,244.6 $ 0.1 $ (4,344.2 ) $ 2,068.0 Liabilities: Accounts payable and other accrued liabilities - contingent liabilities $ — $ — $ 1.0 $ — $ 1.0 TBA and forward settling securities — 4.9 — (0.1 ) 4.8 Derivatives 2,476.2 292.8 — (2,769.0 ) — Payable to broker-dealers, clearing organizations and counterparties - derivatives 2,476.2 297.7 — (2,769.1 ) 4.8 Equity securities 44.0 0.9 — — 44.9 Corporate and municipal bonds 0.3 — — — 0.3 U.S. Treasury obligations 285.9 — — — 285.9 U.S government agency obligations — 27.9 — — 27.9 Agency mortgage-backed obligations — 0.1 — — 0.1 Derivatives — 1,427.2 — (1,110.2 ) 317.0 Commodities leases — 191.1 — (149.6 ) 41.5 Financial instruments sold, not yet purchased 330.2 1,647.2 — (1,259.8 ) 717.6 Total liabilities at fair value $ 2,806.4 $ 1,944.9 $ 1.0 $ (4,028.9 ) $ 723.4 (1) Represents cash collateral and the impact of netting across the levels of the fair value hierarchy. Netting among positions classified within the same level are included in that level.
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block]	The following tables set forth a summary of changes in the fair value of the Company’s Level 3 financial assets and liabilities during the fiscal years ended September 30, 2018 and 2017 , including a summary of unrealized gains (losses) during the fiscal year ended on the Company’s Level 3 financial assets and liabilities held during the periods. Level 3 Financial Assets and Financial Liabilities (in millions) Balances at Realized gains Unrealized Purchases/ Settlements Transfers in Balances at Assets: Equity securities $ 0.1 $ — $ (0.1 ) $ — $ — $ — $ — (in millions) Balances at Realized (gains) Remeasurement Acquisitions Settlements Transfers in Balances at Liabilities: Contingent liabilities $ 1.0 $ — $ — $ — $ (1.0 ) $ — $ — Level 3 Financial Assets and Financial Liabilities (in millions) Balances at Realized gains Unrealized Purchases/ Settlements Transfers in Balances at Assets: Equity securities $ 0.2 $ — $ (0.1 ) $ — $ — $ — $ 0.1 Corporate and municipal bonds 3.0 — — — (3.0 ) — — $ 3.2 $ — $ (0.1 ) $ — $ (3.0 ) $ — $ 0.1 (in millions) Balances at Realized (gains) Remeasurement Acquisitions Settlements Transfers in Balances at Liabilities: Contingent liabilities $ 0.8 $ — $ 0.2 $ — $ — $ — $ 1.0

Financial Instruments with Of_2

Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk (Tables)	12 Months Ended
	Sep. 30, 2018
Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk [Abstract]
Schedule of Derivative Instruments Included in Trading Activities [Table Text Block]	As of September 30, 2018 , TBA and forward settling securities recorded within deposits with and receivables from broker-dealers, clearing organizations, and counterparties are summarized as follows (in millions): Gain / (Loss) Notional Amounts Unrealized gain on TBA securities purchased $ 1.2 $ 721.5 Unrealized loss on TBA securities purchased $ (0.6 ) $ 293.2 Unrealized gain on TBA securities sold $ 3.2 $ (1,099.5 ) Unrealized loss on TBA securities sold $ (1.5 ) $ (812.7 ) Unrealized loss on forward settling securities purchased $ 0.5 $ 614.3 Unrealized gain on forward settling securities sold $ 0.1 $ (427.2 ) The notional amounts of these instruments reflect the extent of the Company’s involvement in TBA and forward settling securities and do not represent counterparty exposure.
Schedule of Derivative Instruments [Table Text Block]	Listed below are the fair values of the Company’s derivative assets and liabilities as of September 30, 2018 and 2017 . Assets represent net unrealized gains and liabilities represent net unrealized losses. September 30, 2018 September 30, 2017 (in millions) Assets (1) Liabilities (1) Assets (1) Liabilities (1) Derivative contracts not accounted for as hedges: Exchange-traded commodity derivatives $ 2,455.7 $ 2,499.3 $ 2,094.2 $ 1,975.0 OTC commodity derivatives 207.0 369.9 1,084.0 1,110.3 Exchange-traded foreign exchange derivatives 49.8 37.2 66.0 52.0 OTC foreign exchange derivatives 302.5 303.9 618.5 609.8 Exchange-traded interest rate derivatives 449.3 478.7 228.4 203.6 OTC interest rate derivatives 24.8 25.9 — — Exchange-traded equity index derivatives 4,541.8 4,794.0 221.3 245.4 TBA and forward settling securities 5.0 2.1 8.8 4.9 Gross fair value of derivative contracts 8,035.9 8,511.0 4,321.2 4,201.0 Impact of netting and collateral (8,118.5 ) (8,317.6 ) (4,205.5 ) (3,879.2 ) Total fair value included in ‘Deposits with and receivables from broker-dealers, clearing organizations and counterparties’ $ (268.7 ) $ (46.4 ) Total fair value included in ‘Financial instruments owned, at fair value’ $ 186.1 $ 162.1 Total fair value included in ‘Payables to broker-dealers, clearing organizations and counterparties $ — $ 4.8 Fair value included in ‘Financial instruments sold, not yet purchased, at fair value’ $ 193.4 $ 317.0 (1) As of September 30, 2018 and 2017 , the Company’s derivative contract volume for open positions was approximately 10.6 million and 6.1 million contracts, respectively.
Schedule of Derivative Instruments, Gain (Loss) in Statement of Financial Performance [Table Text Block]	The following table sets forth the Company’s net gains (losses) related to derivative financial instruments for the fiscal years ended September 30, 2018, 2017, and 2016 , in accordance with the Derivatives and Hedging Topic of the ASC. The net gains (losses) set forth below are included in ‘trading gains, net’ and ‘cost of sales of physical commodities’ in the consolidated income statements. Year Ended September 30, (in millions) 2018 2017 2016 Commodities $ 94.0 $ 47.3 $ 41.8 Foreign exchange 9.2 8.7 9.7 Interest rate and equity 1.0 (0.1 ) 0.8 TBA and forward settling securities 14.5 (2.5 ) (14.4 ) Net gains from derivative contracts $ 118.7 $ 53.4 $ 37.9

Receivables from customers, n_2

Receivables from customers, net and notes receivable, net (Tables)	12 Months Ended
	Sep. 30, 2018
Receivables from customers and notes receivable, net [Abstract]
Allowance for Doubtful Accounts and Notes Receivables [Table Text Block]	Activity in the allowance for doubtful accounts for the years ended September 30, 2018, 2017, and 2016 was as follows: (in millions) 2018 2017 2016 Balance, beginning of year $ 54.6 $ 9.7 $ 11.2 Provision for bad debts 3.9 51.0 4.2 Charge-offs (0.3 ) (6.1 ) (5.7 ) Balance, end of year $ 58.2 $ 54.6 $ 9.7

Physical Commodities Inventor_2

Physical Commodities Inventory Physical Commodities Inventory (Tables)	12 Months Ended
	Sep. 30, 2018
Inventory [Line Items]
Schedule of Inventory, Current [Table Text Block]	(in millions) September 30, September 30, Physical Ag & Energy (1) $ 114.7 $ 65.1 Precious metals - held by broker-dealer subsidiary (2) 42.1 13.3 Precious metals - held by non-broker-dealer subsidiaries (3) 65.7 46.4 Physical commodities inventory $ 222.5 $ 124.8

Property and Equipment, net (Ta

Property and Equipment, net (Tables)	12 Months Ended
	Sep. 30, 2018
Property and Equipment, net [Abstract]
Property, Plant and Equipment [Table Text Block]	A summary of property and equipment, at cost less accumulated depreciation as of September 30, 2018 and 2017 is as follows: (in millions) September 30, 2018 September 30, 2017 Property and equipment: Furniture and fixtures $ 8.7 $ 7.2 Software 30.5 25.3 Equipment 24.7 22.6 Leasehold improvements 17.0 15.4 Total property and equipment 80.9 70.5 Less accumulated depreciation (38.5 ) (31.8 ) Property and equipment, net $ 42.4 $ 38.7

Goodwill (Tables)

Goodwill (Tables)	12 Months Ended
	Sep. 30, 2018
Goodwill [Abstract]
Schedule of Goodwill [Table Text Block]	Goodwill allocated to the Company’s operating segments as of September 30, 2018 and 2017 is as follows: (in millions) September 30, September 30, Commercial Hedging $ 30.3 $ 30.7 Global Payments 8.9 6.3 Physical Commodities 2.4 2.4 Securities 6.8 7.7 Goodwill $ 48.4 $ 47.1

Intangible Assets (Tables)

Intangible Assets (Tables)	12 Months Ended
	Sep. 30, 2018
Intangible Assets [Abstract]
Schedule of Finite and Indefinite-Lived Intangible Assets [Table Text Block]	The gross and net carrying values of intangible assets as of the balance sheet dates, by major intangible asset class are as follows (in millions): September 30, 2018 September 30, 2017 Gross Amount Accumulated Amortization Net Amount Gross Amount Accumulated Amortization Net Amount Intangible assets subject to amortization: Trade name $ — $ — $ — $ — $ — $ — Software programs/platforms 2.7 (2.6 ) 0.1 2.7 (2.5 ) 0.2 Client base 21.4 (10.1 ) 11.3 20.0 (7.9 ) 12.1 Total intangible assets $ 24.1 $ (12.7 ) $ 11.4 $ 22.7 $ (10.4 ) $ 12.3
Schedule of Expected Amortization Expense [Table Text Block]	Amortization expense related to intangible assets was $2.3 million , $2.8 million , and $1.6 million for the fiscal years ended September 30, 2018, 2017, and 2016 , respectively. The estimated future amortization expense as of September 30, 2018 is as follows (in millions): Year ending September 30, 2019 $ 2.5 2020 2.2 2021 2.2 2022 1.0 2023 and thereafter 3.5 $ 11.4

Credit Facilities (Tables)

Credit Facilities (Tables)	12 Months Ended
	Sep. 30, 2018
Credit Facilities [Abstract]
Schedule of Debt [Table Text Block]	The following table sets forth a listing of credit facilities, the current committed amounts, as of the report date, on the facilities, and outstanding borrowings on the facilities as well as indebtedness on a promissory note as of September 30, 2018 and 2017 : (in millions) Credit Facilities Amounts Outstanding Borrower Security Renewal / Expiration Date Total Commitment September 30, September 30, Committed Credit Facilities INTL FCStone Inc. Pledged shares of certain subsidiaries March 18, 2019 $ 262.0 $ 208.2 $ 150.0 INTL FCStone Financial Inc. None April 4, 2019 75.0 — — FCStone Merchants Services, LLC Certain commodities assets November 1, 2019 232.5 128.0 44.2 INTL FCStone Ltd. None January 31, 2019 25.0 — — $ 594.5 336.2 194.2 Uncommitted Credit Facilities INTL FCStone Financial Inc. Commodities warehouse receipts and certain pledged securities n/a — 14.0 34.0 INTL FCStone Ltd. Commodities warehouse receipts n/a — — — FCStone Merchants Services, LLC Certain commodities assets n/a — 3.8 — Note Payable to Bank Monthly installments, due March 2020 and secured by certain equipment 1.2 2.0 Total Payables to lenders under loans $ 355.2 $ 230.2

Commitments and Contingencies F

Commitments and Contingencies Future Minimum Lease Commitments (Tables)	12 Months Ended
	Sep. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Minimum Rental Payments for Operating Leases [Table Text Block]	Future aggregate minimum lease payments under noncancelable operating leases as of September 30, 2018 are as follows: (in millions) Year ending September 30, 2019 $ 10.1 2020 9.3 2021 8.1 2022 5.8 2023 4.5 Thereafter 5.6 $ 43.4

Regulatory Requirements and S_2

Regulatory Requirements and Subsidiary Dividend Restrictions (Tables)	12 Months Ended
	Sep. 30, 2018
Capital and Other Regulatory Requirements [Abstract]
Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations [Table Text Block]	All subsidiaries of the Company are in compliance with all of their regulatory requirements as of September 30, 2018 , as follows: (in millions) As of September 30, 2018 Subsidiary Regulatory Authority Requirement Type Actual Minimum Requirement INTL FCStone Financial Inc. SEC and CFTC Net capital $ 167.7 $ 101.4 INTL FCStone Financial Inc. CFTC Segregated funds $ 2,637.0 $ 2,579.7 INTL FCStone Financial Inc. CFTC Secured funds $ 148.9 $ 132.8 INTL FCStone Financial Inc. SEC Customer reserve * $ 6.4 INTL FCStone Financial Inc. SEC PAB reserve $ 0.3 $ — SA Stone Wealth Management Inc. SEC Net capital $ 4.6 $ 0.4 INTL FCStone Ltd FCA (United Kingdom) Net capital $ 193.1 $ 95.9 INTL FCStone Ltd FCA (United Kingdom) Segregated funds $ 187.3 $ 182.1 INTL Netherlands BV FCA (United Kingdom) Net capital $ 193.0 $ 95.9 INTL FCStone DTVM Ltda. Brazilian Central Bank and Securities and Exchange Commission of Brazil Capital adequacy $ 11.2 $ 2.1 INTL Gainvest S.A. National Securities Commission ("CNV") Capital adequacy $ 4.2 $ 0.1 INTL Gainvest S.A. CNV Net capital $ 1.2 $ 0.1 INTL CIBSA S.A. CNV Capital adequacy $ 4.4 $ 0.5 INTL CIBSA S.A. CNV Net capital $ 3.1 $ 0.3

Commodity and Other Repurchas_2

Commodity and Other Repurchase Agreements Gross Obligations Contractual Maturities (Tables)	12 Months Ended
	Sep. 30, 2018
Assets Sold under Agreements to Repurchase [Line Items]
Schedule of Underlying Assets of Repurchase Agreements when Amount of Repurchase Agreements Exceeds 10 Percent of Assets [Table Text Block]	September 30, 2018 Overnight and Open Less than 30 Days 30-90 Days Total Securities sold under agreements to repurchase $ 934.9 $ 661.3 $ 340.5 $ 1,936.7 Securities loaned 277.9 — — 277.9 Gross amount of secured financing $ 1,212.8 $ 661.3 $ 340.5 $ 2,214.6 September 30, 2017 Overnight and Open Less than 30 Days 30-90 Days Total Securities sold under agreements to repurchase $ 640.2 $ 432.9 $ 320.0 $ 1,393.1 Securities loaned 111.1 — — 111.1 Gross amount of secured financing $ 751.3 $ 432.9 $ 320.0 $ 1,504.2

Commodity and Other Repurchas_3

Commodity and Other Repurchase Agreements Gross Obligations Collateral Types (Tables)	12 Months Ended
	Sep. 30, 2018
Financial Instruments Owned and Pledged as Collateral [Line Items]
Schedule of Financial Instruments Owned and Pledged as Collateral [Table Text Block]	Securities sold under agreements to repurchase: September 30, 2018 September 30, 2017 U.S. Treasury obligations $ 39.6 $ 7.0 U.S. government agency obligations 461.7 332.6 Asset-backed obligations 50.0 36.4 Agency mortgage-backed obligations 1,385.4 1,017.1 Total securities sold under agreements to repurchase $ 1,936.7 $ 1,393.1 Securities loaned: Equity securities 277.9 111.1 Total securities loaned 277.9 111.1 Gross amount of secured financing $ 2,214.6 $ 1,504.2

Share-Based Compensation (Table

Share-Based Compensation (Tables)	12 Months Ended
	Sep. 30, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]	Fair value is estimated at the grant date based on a Black-Scholes-Merton option-pricing model using the following weighted-average assumptions: Year Ended September 30, 2018 2017 2016 Expected stock price volatility 30 % 31 % 28 % Expected dividend yield — % — % — % Risk free interest rate 1.23 % 0.99 % 0.83 % Average expected life (in years) 3.06 3.08 3.06
Share-based Compensation, Stock Options, Activity [Table Text Block]	The following is a summary of stock option activity for the year ended September 30, 2018 : Shares Available for Grant Number of Options Outstanding Weighted Average Exercise Price Weighted Average Grant Date Fair Value Weighted Average Remaining Term (in years) Aggregate Intrinsic Value ($ millions) Balances at September 30, 2017 652,494 881,403 $ 27.31 $ 11.55 3.57 $ 9.8 Granted (79,800 ) 79,800 $ 44.17 $ 9.79 Exercised (110,423 ) $ 23.79 $ 7.98 Forfeited 13,324 (13,324 ) $ 33.19 $ 7.14 Expired 2,002 (2,002 ) $ 32.60 $ 6.78 Balances at September 30, 2018 588,020 835,454 $ 29.27 $ 11.93 3.01 $ 15.9 Exercisable at September 30, 2018 314,366 $ 27.16 $ 11.68 2.81 $ 6.7
Schedule of Share-based Compensation, Shares Authorized under Stock Option Plans, by Exercise Price Range [Table Text Block]	The options outstanding as of September 30, 2018 broken down by exercise price are as follows: Exercise Price Number of Options Outstanding Weighted Average Exercise Price Weighted Average Remaining Term $ — - $ 5.00 — n/a n/a $ 5.00 - $ 10.00 — n/a n/a $ 10.00 - $ 15.00 — n/a n/a $ 15.00 - $ 20.00 — n/a n/a $ 20.00 - $ 25.00 28,668 $ 20.54 0.27 $ 25.00 - $ 30.00 580,000 $ 25.91 3.37 $ 30.00 - $ 35.00 49,656 $ 31.37 1.28 $ 35.00 - $ 40.00 100,330 $ 38.77 2.27 $ 40.00 - $ 45.00 74,800 $ 43.88 3.30 $ 45.00 - $ 50.00 — n/a n/a $ 50.00 - $ 55.00 2,000 $ 55.28 3.89 835,454 $ 29.27 3.01
Schedule of Share-based Compensation, Restricted Stock Units Award Activity [Table Text Block]	The following is a summary of restricted stock activity through September 30, 2018 : Shares Available for Grant Number of Shares Outstanding Weighted Average Grant Date Fair Value Weighted Average Remaining Term (in years) Aggregate Intrinsic Value ($ millions) Balances at September 30, 2017 1,459,976 354,474 $ 33.34 1.26 $ 13.6 Granted (85,404 ) 85,404 $ 44.86 Vested (162,544 ) $ 31.14 Forfeited 2,706 (2,706 ) $ 36.24 Balances at September 30, 2018 1,377,278 274,628 $ 38.20 1.15 $ 13.3

Other Expenses (Tables)

Other Expenses (Tables)	12 Months Ended
	Sep. 30, 2018
Other Expenses [Abstract]
Schedule of Other Operating Cost and Expense, by Component [Table Text Block]	Other expenses for the years ended September 30, 2018, 2017, and 2016 are comprised of the following: Year Ended September 30, (in millions) 2018 2017 2016 Contingent consideration, net (1) $ — $ 0.1 $ 0.4 Insurance 2.6 2.7 2.1 Advertising, meetings and conferences 6.2 4.0 5.1 Office supplies and printing 1.7 2.1 1.2 Other clearing related expenses 2.5 2.6 1.3 Other non-income taxes 4.9 4.6 4.3 Other 8.4 9.8 7.9 Total other expenses $ 26.3 $ 25.9 $ 22.3 (1) Contingent consideration includes remeasurement of contingent liabilities related to business combinations accounted for in accordance with the provisions of the Business Combinations Topic of the ASC (see Note 3 ).

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Schedule of Components of Income Tax Expense (Benefit) [Table Text Block]	Income tax expense (benefit) for the years ended September 30, 2018, 2017, and 2016 was allocated as follows: Year Ended September 30, (in millions) 2018 2017 2016 Income tax expense attributable to income from operations $ 46.0 $ 8.8 $ 18.0 Taxes allocated to stockholders’ equity, related to pension liabilities 0.1 1.0 0.2 Taxes allocated to additional paid-in capital, related to share-based compensation — 0.1 (0.8 ) Total income tax expense $ 46.1 $ 9.9 $ 17.4 The components of income tax expense (benefit) attributable to income from operations were as follows: Year Ended September 30, (in millions) 2018 2017 2016 Current taxes: U.S. federal $ 0.8 $ 0.7 $ 1.3 U.S. State and local 0.5 1.2 0.8 International 22.4 16.7 16.8 Total current taxes 23.7 18.6 18.9 Deferred taxes 22.3 (9.8 ) (0.8 ) Income tax benefit attributable to interest income — — (0.1 ) Income tax expense $ 46.0 $ 8.8 $ 18.0
Schedule of Income before Income Tax, Domestic and Foreign [Table Text Block]	U.S. and international components of (loss) income from operations, before tax, was as follows: Year Ended September 30, (in millions) 2018 2017 2016 U.S. $ 9.9 $ (13.9 ) $ 4.8 International 91.6 29.1 67.9 Income from operations, before tax $ 101.5 $ 15.2 $ 72.7
Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]	Items accounting for the difference between income taxes computed at the federal statutory rate and income tax expense were as follows: Year Ended September 30, 2018 2017 2016 Federal statutory rate effect of: 24.5 % 35.0 % 35.0 % U.S. State and local income taxes 0.8 % (2.6 )% 1.3 % Foreign earnings and losses taxed at lower rates (0.8 )% 11.5 % (11.0 )% Change in foreign valuation allowance (0.8 )% (1.4 )% (0.3 )% Change in state valuation allowance — % 4.1 % — % U.S. permanent items (0.2 )% 3.6 % 0.8 % Foreign permanent items 2.1 % 8.1 % 1.9 % U.S. bargain purchase gain — % — % (3.0 )% Remeasurement of deferred tax 8.5 % — % — % Repatriation Transition tax 11.0 % — % — % Other reconciling items 0.2 % (0.6 )% 0.3 % Effective rate 45.3 % 57.7 % 25.0 %
Schedule of Deferred Tax Assets and Liabilities [Table Text Block]	The components of deferred income tax assets and liabilities were as follows: (in millions) September 30, 2018 September 30, 2017 Deferred tax assets: Share-based compensation $ 2.8 $ 3.7 Pension liability — 0.1 Deferred compensation 1.4 2.0 Foreign net operating loss carryforwards 4.2 5.6 U.S. State and local net operating loss carryforwards 8.7 6.6 U.S. federal net operating loss carryforwards — 21.9 Intangible assets 1.8 6.1 Bad debt reserve 1.5 1.4 Tax credit carryforwards — 1.6 Foreign tax credit carryforwards 6.5 — Other compensation 3.4 3.6 Other 0.9 1.9 Total gross deferred tax assets 31.2 54.5 Less valuation allowance (3.5 ) (4.0 ) Deferred tax assets 27.7 50.5 Deferred income tax liabilities: Unrealized gain on securities 2.6 3.2 Prepaid expenses 1.8 2.5 Property and equipment 3.1 2.2 Pension liability 0.4 — Deferred income tax liabilities 7.9 7.9 Deferred income taxes, net $ 19.8 $ 42.6
Summary of Income Tax Contingencies [Table Text Block]	A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows: Year Ended September 30, (in millions) 2018 2017 2016 Balance, beginning of year $ 0.1 $ 0.1 $ — Gross increases for tax positions related to prior years — — 0.1 Balance, end of year $ 0.1 $ 0.1 $ 0.1

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Income (Loss) (Tables)	12 Months Ended
	Sep. 30, 2018
Accumulated Other Comprehensive Income (Loss) [Abstract]
Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block]	The following table summarizes the changes in accumulated other comprehensive (loss) income for the year ended September 30, 2018 . (in millions) Foreign Currency Translation Adjustment Pension Benefits Adjustment Accumulated Other Comprehensive Loss Balances as of September 30, 2017 $ (21.5 ) $ (3.0 ) $ (24.5 ) Other comprehensive (loss) income, net of tax before reclassifications (9.0 ) 0.3 (8.7 ) Amounts reclassified from AOCI, net of tax — 0.1 0.1 Other comprehensive (loss) income, net of tax (9.0 ) 0.4 (8.6 ) Balances as of September 30, 2018 $ (30.5 ) $ (2.6 ) $ (33.1 )

Quarterly Financial Informati_2

Quarterly Financial Information (Unaudited) (Tables)	12 Months Ended
	Sep. 30, 2018
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Information [Table Text Block]	The Company has set forth certain quarterly unaudited financial data for the past two years in the tables below: For the 2018 Fiscal Quarter Ended (in millions, except per share amounts) September 30 (1) June 30 March 31 December 31 Total revenues $ 6,078.8 $ 7,118.3 $ 6,507.0 $ 7,918.6 Cost of sales of physical commodities 5,835.6 6,858.5 6,246.8 7,706.0 Operating revenues 243.2 259.8 260.2 212.6 Transaction-based clearing expenses 43.1 49.0 50.7 36.9 Introducing broker commissions 32.4 34.1 36.2 31.1 Interest expense 25.3 22.1 19.0 14.3 Net operating revenues 142.4 154.6 154.3 130.3 Compensation and benefits 85.4 86.9 88.2 77.2 Bad debts 1.2 1.6 0.2 0.1 Bad debt on physical coal (1) — — — 1.0 Other expenses 35.3 35.2 36.4 33.4 Total compensation and other expenses 121.9 123.7 124.8 111.7 Other gain — 2.0 — — Income before tax 20.5 32.9 29.5 18.6 Income tax expense 4.8 8.9 6.8 25.5 Net income (loss) $ 15.7 $ 24.0 $ 22.7 $ (6.9 ) Net basic earnings (loss) per share $ 0.83 $ 1.27 $ 1.20 $ (0.37 ) Net diluted earnings (loss) per share $ 0.81 $ 1.25 $ 1.18 $ (0.37 ) For the 2017 Fiscal Quarter Ended (in millions, except per share amounts) September 30 June 30 March 31 December 31 Total revenues $ 12,382.5 $ 5,505.9 $ 5,460.8 $ 6,074.4 Cost of sales of physical commodities 12,177.4 5,308.3 5,265.0 5,888.9 Operating revenues 205.1 197.6 195.8 185.5 Transaction-based clearing expenses 35.1 33.9 33.7 33.6 Introducing broker commissions 26.9 29.2 28.2 28.7 Interest expense 12.0 11.2 10.0 8.9 Net operating revenues 131.1 123.3 123.9 114.3 Compensation and benefits 73.0 75.5 76.6 70.6 Bad debts 0.4 0.1 1.3 2.5 Bad debt on physical coal (1) 47.0 — — — Other expenses 33.2 32.7 31.7 32.8 Total compensation and other expenses 153.6 108.3 109.6 105.9 Income before tax (22.5 ) 15.0 14.3 8.4 Income tax expense 1.1 2.3 3.3 2.1 Net income $ (23.6 ) $ 12.7 $ 11.0 $ 6.3 Net basic (loss) earnings per share $ (1.27 ) $ 0.67 $ 0.58 $ 0.34 Net diluted (loss) earnings per share $ (1.27 ) $ 0.66 $ 0.58 $ 0.34

Segment and Geographic Inform_2

Segment and Geographic Information (Tables)	12 Months Ended
	Sep. 30, 2018
Segment Analysis [Abstract]
Schedule of Segment Reporting Information, by Segment [Table Text Block]	Information concerning operations in these segments of business is shown in accordance with the Segment Reporting Topic of the ASC as follows: Year Ended September 30, (in millions) 2018 2017 2016 Total revenues: Commercial Hedging $ 286.7 $ 244.6 $ 236.1 Global Payments 99.2 89.2 73.2 Securities 196.2 151.7 175.2 Physical Commodities 26,703.8 28,684.4 14,120.5 Clearing and Execution Services 332.4 259.8 151.1 Corporate unallocated 4.4 (6.1 ) (1.2 ) Total $ 27,622.7 $ 29,423.6 $ 14,754.9 Operating revenues (loss): Commercial Hedging $ 286.7 $ 244.6 $ 236.1 Global Payments 99.2 89.2 73.2 Securities 196.2 151.7 175.2 Physical Commodities 56.9 44.8 36.6 Clearing and Execution Services 332.4 259.8 151.1 Corporate unallocated 4.4 (6.1 ) (1.2 ) Total $ 975.8 $ 784.0 $ 671.0 Net operating revenues (loss): Commercial Hedging $ 226.4 $ 194.3 $ 188.2 Global Payments 93.5 80.6 65.3 Securities 94.6 94.6 121.9 Physical Commodities 44.8 37.3 31.5 Clearing and Execution Services 122.6 102.2 48.8 Corporate unallocated (0.3 ) (16.4 ) (11.8 ) Total $ 581.6 $ 492.6 $ 443.9 Net contribution: (Revenues less cost of sales, transaction-based clearing expenses, variable bonus compensation, introducing broker commissions and interest expense): Commercial Hedging $ 164.7 $ 141.8 $ 134.4 Global Payments 75.0 64.4 52.2 Securities 69.1 75.6 97.5 Physical Commodities 31.8 27.2 23.4 Clearing and Execution Services 91.8 78.0 39.5 Total $ 432.4 $ 387.0 $ 347.0 Segment income (loss): (Net contribution less non-variable direct segment costs): Commercial Hedging $ 96.4 $ 72.8 $ 68.7 Global Payments 59.8 50.6 39.8 Securities 40.8 46.6 69.4 Physical Commodities (1) 16.6 (31.4 ) 13.3 Clearing and Execution Services 48.3 30.4 14.8 Total $ 261.9 $ 169.0 $ 206.0 Reconciliation of segment income to income before tax: Segment income $ 261.9 $ 169.0 $ 206.0 Costs not allocated to operating segments (2) 162.4 153.8 139.5 Other gains 2.0 — 6.2 Income before tax $ 101.5 $ 15.2 $ 72.7 (1) During the first quarter of fiscal 2018 and the fourth quarter of fiscal 2017, the Company recorded charges to earnings of $1.0 million and $47.0 million , respectively, to record an allowance for doubtful accounts related to a bad debt incurred in the physical coal business conducted solely in INTL Asia Pte. Ltd., with a coal supplier, as further discussed in Note 17 . (2) The costs not allocated to operating segments include certain shared services such as information technology, accounting and treasury, credit and risk, legal and compliance, and human resources and other activities. (in millions) As of September 30, 2018 As of September 30, 2017 As of September 30, 2016 Total assets: Commercial Hedging $ 1,935.7 $ 1,650.3 $ 1,637.5 Global Payments 206.6 199.5 191.4 Securities 3,058.2 2,101.7 2,130.7 Physical Commodities 413.7 339.5 258.0 Clearing and Execution Services 2,109.9 1,818.9 1,617.4 Corporate unallocated 100.6 133.5 115.3 Total $ 7,824.7 $ 6,243.4 $ 5,950.3
Schedule of Revenue from External Customers and Long-Lived Assets, by Geographical Areas [Table Text Block]	Information regarding revenues and operating revenues for the years ended September 30, 2018, 2017, and 2016 , and information regarding long-lived assets (defined as property, equipment, leasehold improvements and software) as of September 30, 2018, 2017, and 2016 in geographic areas were as follows: Year Ended September 30, (in millions) 2018 2017 2016 Total revenues: United States $ 1,587.6 $ 1,168.0 $ 817.1 Europe 189.6 166.9 463.5 South America 59.5 53.9 64.8 Asia 25,781.4 28,030.3 13,405.1 Other 4.6 4.5 4.4 Total $ 27,622.7 $ 29,423.6 $ 14,754.9 Operating revenues: United States $ 695.3 $ 529.4 $ 457.0 Europe 189.0 166.9 120.2 South America 58.0 54.0 64.8 Asia 28.9 29.2 24.6 Other 4.6 4.5 4.4 Total $ 975.8 $ 784.0 $ 671.0 (in millions) As of September 30, 2018 As of September 30, 2017 As of September 30, 2016 Long-lived assets, as defined: United States $ 33.0 $ 29.7 $ 23.3 Europe 6.8 7.3 4.8 South America 1.4 1.5 1.2 Asia 1.2 0.2 0.1 Total $ 42.4 $ 38.7 $ 29.4

Description of Business and S_3

Description of Business and Significant Accounting Policies - Accounts, Customers and Other Facts (Details)	12 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Number of different types of foreign currencies	140
Number of accounts for customers company-wide	20,000

Description of Business and S_4

Description of Business and Significant Accounting Policies - Cash, Cash Equivalents, Securities (Details) - USD ($)	Sep. 30, 2018	Sep. 30, 2017
Accounting Policies [Abstract]
Cash Held at Banks and Money Market Funds - Segregated	$ 765,400,000	$ 464,300,000
US Government Obligations and other securities	600,400,000	33,500,000
Commodities Warehouse Receipts	42,900,000	21,000,000
Cash and Cash Equivalents - Deposits and Receivables	1,500,000,000	2,300,000,000
US Government Securities and Other Securities - Deposits and Receivables	785,753,569	300,000,000
Memberships in Exchanges Owned	11,400,000	12,000,000
Fair Value of Exchange Memberships	$ 10,300,000	$ 10,200,000

Description of Business and S_5

Description of Business and Significant Accounting Policies - Basis of Presentation and Consolidation (Details) - USD ($)	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2018
Memberships in Exchanges Owned	$ 12,000,000		$ 11,400,000
Fair Value of Exchange Memberships	10,200,000		10,300,000
Cash and Cash Equivalents - Deposits and Receivables	$ 2,300,000,000		$ 1,500,000,000
Preferred Stock, Par or Stated Value Per Share	$ 0.01		$ 0.01
Preferred Stock, Shares Outstanding	0		0
US Government Securities and Other Securities - Deposits and Receivables	$ 300,000,000		$ 785,753,569
Non-Trading Technology and Support [Member]
Prior Period Reclassification Adjustment	11,600,000	$ 7,100,000
communications [Member]
Prior Period Reclassification Adjustment	$ 5,000,000	$ 4,700,000

Earnings per Share - EPS Reconc

Earnings per Share - EPS Reconciliation (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share [Abstract]
Income from Continuing Operations	$ 55.5	$ 6.4	$ 54.7
Undistributed Earnings Allocated to Participating Securities - Continuing Operations	(0.9)	(0.1)	(1)
Income from continuing operations allocated to common shareholders	$ 54.6	$ 6.3	$ 53.7
Weighted Average Number of Shares Outstanding, Basic	18,549,011	18,395,987	18,410,561
Dilutive Securities, Effect on Basic Earnings Per Share [Abstract]
Share-based Awards For Diluted Earnings Per Share Calculation	385,819	291,367	214,811
Diluted weighted-average shares	18,934,830	18,687,354	18,625,372

Earnings per Share - Antiduliti

Earnings per Share - Antidulitive Securities (Details) - shares	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share [Abstract]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	92,627	230,135	910,060

Assets and Liabilities, at Fa_3

Assets and Liabilities, at Fair Value - Financial Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Securities Segregated under Federal and Other Regulations	$ 1,408.7	$ 518.8
Receivables from Brokers-Dealers and Clearing Organizations	2,234.5	2,625.1
Financial instruments owned, at fair value	2,054.8	1,731.8
Accounts payable and other accrued liabilities	145.4	135.6
Payables to Broker-Dealers and Clearing Organizations	(89.5)	(125.7)
Financial Instruments Sold, Not yet Purchased, at Fair Value	866.5	717.6
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure		3.8
Cash and Securities Segregated under Federal and Other Regulations	643.3	54.5
Receivables from Clearing Organizations		204.7
Receivables from Brokers-Dealers and Clearing Organizations	517.4
Financial instruments owned, at fair value	2,054.8	1,731.8
Assets, Fair Value Disclosure	3,376.2	2,068
Payables to Broker-Dealers and Clearing Organizations	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	866.5	717.6
Liabilities, Fair Value Disclosure	866.5	723.4
Fair Value, Measurements, Recurring [Member] | TBA and forward settling securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payables to Broker-Dealers and Clearing Organizations	0	(4.8)
Fair Value, Measurements, Recurring [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payables to Broker-Dealers and Clearing Organizations	0	0
Fair Value, Measurements, Recurring [Member] | Contingent Consideration [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Accounts payable and other accrued liabilities	0	1
Fair Value, Measurements, Recurring [Member] | Physical commodities inventory[Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Physical Commodities Inventory	156.9	73.2
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	74.2	45.1
Financial Instruments Sold, Not yet Purchased, at Fair Value	51.5	44.9
Fair Value, Measurements, Recurring [Member] | Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	42.9	47.3
Fair Value, Measurements, Recurring [Member] | US Government Agencies Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	472.9	368.9
Financial Instruments Sold, Not yet Purchased, at Fair Value	57.2
Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	79.1	29.1
Financial Instruments Sold, Not yet Purchased, at Fair Value	20.1	0.3
Fair Value, Measurements, Recurring [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	120.1	60
Financial Instruments Sold, Not yet Purchased, at Fair Value	484.8	285.9
Fair Value, Measurements, Recurring [Member] | Foreign Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	6.4	10.2
Financial Instruments Sold, Not yet Purchased, at Fair Value		27.9
Fair Value, Measurements, Recurring [Member] | Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	1,022.5	920.9
Financial Instruments Sold, Not yet Purchased, at Fair Value	0.2	0.1
Fair Value, Measurements, Recurring [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	186.1	162.1
Financial Instruments Sold, Not yet Purchased, at Fair Value	193.4	317
Fair Value, Measurements, Recurring [Member] | Commodities leases and unpriced positions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	17.7	35.4
Financial Instruments Sold, Not yet Purchased, at Fair Value	59.3	41.5
Fair Value, Measurements, Recurring [Member] | Commodities warehouse receipts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	16.4	38.5
Fair Value, Measurements, Recurring [Member] | Exchange firm common stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	10.2
Fair Value, Measurements, Recurring [Member] | Mutual funds and other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	6.3	6
Fair Value, Measurements, Recurring [Member] | Foreign Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Brokers-Dealers and Clearing Organizations	7.7
Fair Value, Measurements, Recurring [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Brokers-Dealers and Clearing Organizations	778.4
Fair Value, Measurements, Recurring [Member] | TBA and forward settling securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Brokers-Dealers and Clearing Organizations	2.9
Fair Value, Measurements, Recurring [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payables to Broker-Dealers and Clearing Organizations	(271.6)
Fair Value, Measurements, Recurring [Member] | Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations		8.8
Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations		6.4
Fair Value, Measurements, Recurring [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations		244.7
Fair Value, Measurements, Recurring [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payables to Broker-Dealers and Clearing Organizations		(55.2)
Fair Value, Measurements, Recurring [Member] | Commodities warehouse receipts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Securities Segregated under Federal and Other Regulations	42.9	21
Fair Value, Measurements, Recurring [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Securities Segregated under Federal and Other Regulations	600.4	33.5
Fair Value, Measurements, Recurring [Member] | Certificates of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	3.8
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure		3.8
Cash and Securities Segregated under Federal and Other Regulations	643.3	54.5
Receivables from Clearing Organizations		2,853.3
Receivables from Brokers-Dealers and Clearing Organizations	8,282
Financial instruments owned, at fair value	231.4	182.7
Assets, Fair Value Disclosure	9,202.6	3,167.5
Payables to Broker-Dealers and Clearing Organizations	(7,809.3)
Financial Instruments Sold, Not yet Purchased, at Fair Value	535.9	330.2
Liabilities, Fair Value Disclosure	8,345.2	2,806.4
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | TBA and forward settling securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payables to Broker-Dealers and Clearing Organizations	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payables to Broker-Dealers and Clearing Organizations	(7,809.3)	(2,476.2)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Contingent Consideration [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Accounts payable and other accrued liabilities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Physical commodities inventory[Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Physical Commodities Inventory	42.1	73.2
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	71.2	40.4
Financial Instruments Sold, Not yet Purchased, at Fair Value	51.1	44
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | US Government Agencies Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	0	28.2
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0.3
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	120.1	60
Financial Instruments Sold, Not yet Purchased, at Fair Value	484.8	285.9
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Foreign Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	6.4	0
Financial Instruments Sold, Not yet Purchased, at Fair Value		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	0.8	1.3
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Commodities leases and unpriced positions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Commodities warehouse receipts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	16.4	38.5
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Exchange firm common stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	10.2	8.3
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Mutual funds and other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	6.3	6
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Foreign Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Brokers-Dealers and Clearing Organizations	7.7
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Brokers-Dealers and Clearing Organizations	778.4
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | TBA and forward settling securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Brokers-Dealers and Clearing Organizations	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Brokers-Dealers and Clearing Organizations	7,495.9
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations		244.7
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations		2,608.6
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Commodities warehouse receipts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Securities Segregated under Federal and Other Regulations	42.9	21
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Securities Segregated under Federal and Other Regulations	600.4	33.5
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Certificates of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	3.8
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure		0
Cash and Securities Segregated under Federal and Other Regulations	0	0
Receivables from Clearing Organizations		304.3
Receivables from Brokers-Dealers and Clearing Organizations	24.6
Financial instruments owned, at fair value	2,164.5	2,940.3
Assets, Fair Value Disclosure	2,303.9	3,244.6
Payables to Broker-Dealers and Clearing Organizations	(13.7)
Financial Instruments Sold, Not yet Purchased, at Fair Value	841.4	1,647.2
Liabilities, Fair Value Disclosure	855.1	1,944.9
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | TBA and forward settling securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payables to Broker-Dealers and Clearing Organizations	(2.1)	(4.9)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payables to Broker-Dealers and Clearing Organizations	(11.6)	(292.8)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Contingent Consideration [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Accounts payable and other accrued liabilities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Physical commodities inventory[Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Physical Commodities Inventory	114.8	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	3	4.6
Financial Instruments Sold, Not yet Purchased, at Fair Value	0.4	0.9
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	42.9	47.3
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | US Government Agencies Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	472.9	368.9
Financial Instruments Sold, Not yet Purchased, at Fair Value	57.2
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	79.1	0.9
Financial Instruments Sold, Not yet Purchased, at Fair Value	20.1	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Foreign Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	0	10.2
Financial Instruments Sold, Not yet Purchased, at Fair Value		27.9
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	1,022.5	920.9
Financial Instruments Sold, Not yet Purchased, at Fair Value	0.2	0.1
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	514.6	1,413.4
Financial Instruments Sold, Not yet Purchased, at Fair Value	688	1,427.2
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Commodities leases and unpriced positions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	29.5	174.1
Financial Instruments Sold, Not yet Purchased, at Fair Value	75.5	191.1
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Commodities warehouse receipts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Exchange firm common stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Mutual funds and other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Foreign Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Brokers-Dealers and Clearing Organizations	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Brokers-Dealers and Clearing Organizations	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | TBA and forward settling securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Brokers-Dealers and Clearing Organizations	5
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Brokers-Dealers and Clearing Organizations	19.6
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations		8.8
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations		6.4
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations		289.1
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Commodities warehouse receipts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Securities Segregated under Federal and Other Regulations	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Securities Segregated under Federal and Other Regulations	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Certificates of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure		0
Cash and Securities Segregated under Federal and Other Regulations	0	0
Receivables from Clearing Organizations		0
Receivables from Brokers-Dealers and Clearing Organizations	0
Financial instruments owned, at fair value	0	0.1
Assets, Fair Value Disclosure	0	0.1
Payables to Broker-Dealers and Clearing Organizations	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Liabilities, Fair Value Disclosure	0	1
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | TBA and forward settling securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payables to Broker-Dealers and Clearing Organizations	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payables to Broker-Dealers and Clearing Organizations	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Contingent Consideration [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Accounts payable and other accrued liabilities	0	1
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Physical commodities inventory[Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Physical Commodities Inventory	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	0	0.1
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | US Government Agencies Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Foreign Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Commodities leases and unpriced positions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Commodities warehouse receipts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Exchange firm common stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Mutual funds and other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Foreign Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Brokers-Dealers and Clearing Organizations	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Brokers-Dealers and Clearing Organizations	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | TBA and forward settling securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Brokers-Dealers and Clearing Organizations	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Brokers-Dealers and Clearing Organizations	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Commodities warehouse receipts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Securities Segregated under Federal and Other Regulations	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Securities Segregated under Federal and Other Regulations	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Certificates of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	0
Derivative [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payables to Broker-Dealers and Clearing Organizations		(4.8)
Derivative [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payables to Broker-Dealers and Clearing Organizations		(2,476.2)
Derivative [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payables to Broker-Dealers and Clearing Organizations		(297.7)
Derivative [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payables to Broker-Dealers and Clearing Organizations		0
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure		0
Cash and Securities Segregated under Federal and Other Regulations	0	0
Receivables from Clearing Organizations		(2,952.9)
Receivables from Brokers-Dealers and Clearing Organizations	(7,789.2)
Financial instruments owned, at fair value	(341.1)	(1,391.3)
Assets, Fair Value Disclosure	(8,130.3)	(4,344.2)
Payables to Broker-Dealers and Clearing Organizations	7,823
Financial Instruments Sold, Not yet Purchased, at Fair Value	(510.8)	(1,259.8)
Liabilities, Fair Value Disclosure	(8,333.8)	(4,028.9)
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member] | TBA and forward settling securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payables to Broker-Dealers and Clearing Organizations	2.1	0.1
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payables to Broker-Dealers and Clearing Organizations	7,820.9	2,769
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member] | Contingent Consideration [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Accounts payable and other accrued liabilities	0	0
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member] | Physical commodities inventory[Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Physical Commodities Inventory	0	0
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member] | Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	0	0
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member] | US Government Agencies Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member] | Foreign Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value		0
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member] | Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	(329.3)	(1,252.6)
Financial Instruments Sold, Not yet Purchased, at Fair Value	(494.6)	(1,110.2)
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member] | Commodities leases and unpriced positions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	(11.8)	(138.7)
Financial Instruments Sold, Not yet Purchased, at Fair Value	(16.2)	(149.6)
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member] | Commodities warehouse receipts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	0	0
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member] | Exchange firm common stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	0	0
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member] | Mutual funds and other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	0	0
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member] | Foreign Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Brokers-Dealers and Clearing Organizations	0
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Brokers-Dealers and Clearing Organizations	0
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member] | TBA and forward settling securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Brokers-Dealers and Clearing Organizations	(2.1)
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Brokers-Dealers and Clearing Organizations	(7,787.1)
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member] | Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations		0
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations		0
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations		0
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations		(2,952.9)
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member] | Commodities warehouse receipts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Securities Segregated under Federal and Other Regulations	0	0
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Securities Segregated under Federal and Other Regulations	0	0
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member] | Certificates of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	$ 0
Counterparty And Cash Collateral Netting Adjustment [Member] | Derivative [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payables to Broker-Dealers and Clearing Organizations		$ 2,769.1

Assets and Liabilities, at Fa_4

Assets and Liabilities, at Fair Value - Rollforward of Level 3 (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Rollforward of Level 3 Liabilities [Roll Forward]
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability	$ 0	$ (0.2)	$ (0.4)
Contingent Consideration [Member]
Rollforward of Level 3 Liabilities [Roll Forward]
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value	1	0.8
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Period Increase (Decrease)	0	0.2
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Purchases	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements	(1)	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Transfers, Net	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value	0	1	0.8
Equity Securities [Member]
Rollforward of Level 3 Assets [Roll Forward]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	0.1	0.2
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Period Increase (Decrease)	(0.1)	(0.1)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers, Net	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	0	0.1	0.2
Corporate Debt Securities [Member]
Rollforward of Level 3 Assets [Roll Forward]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	$ 0	3
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Period Increase (Decrease)		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements		(3)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers, Net		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		$ 0	$ 3

Assets and Liabilities, at Fa_5

Assets and Liabilities, at Fair Value - Suriwongse Bonds (Details) $ in Millions	Sep. 30, 2016USD ($)
Corporate Debt Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Financial Instruments, Owned, Corporate Debt, at Fair Value	$ 3

Assets and Liabilities, at Fa_6

Assets and Liabilities, at Fair Value - Contingent Consideration (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability	$ 0	$ 0.1	$ 0.4
Payment for Contingent Consideration Liability, Financing Activities	$ 1

Assets and Liabilities, at Fa_7

Assets and Liabilities, at Fair Value - Available for Sale Securities in OCI (Details) - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017
Assets and Liabilities, at Fair Value [Abstract]
Equity Investments in Exchange Stock - Cost	$ 3.7	$ 3.9
Equity Investments in Exchange Stock - Fair Value	$ 10.2	$ 8.3

Financial Instruments with Of_3

Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk - Obligations to Purchase Financial Instruments at a Future Date (Details) - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017
Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk [Abstract]
Financial Instruments Sold, Not yet Purchased, at Fair Value	$ 866.5	$ 717.6
Derivative, Fair Value, Net	$ 193.4

Financial Instruments with Of_4

Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk - Gross Derivative Assets and Liabilities by Type and Balance Sheet Location (Details) - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 8,035.9	$ 4,321.2
Derivative Liability, Fair Value, Gross Liability	8,511	4,201
Derivative, Fair Value, Net	193.4
Exchange-traded Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	2,455.7	2,094.2
Derivative Liability, Fair Value, Gross Liability	2,499.3	1,975
Over the Counter (OTC) Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	207	1,084
Derivative Liability, Fair Value, Gross Liability	369.9	1,110.3
Foreign Exchange Forward [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	49.8	66
Derivative Liability, Fair Value, Gross Liability	37.2	52
Over the Counter (OTC) Foreign Exchange Contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	302.5	618.5
Derivative Liability, Fair Value, Gross Liability	303.9	609.8
Exchange-traded interest rate contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	449.3	228.4
Derivative Liability, Fair Value, Gross Liability	478.7	203.6
Interest Rate Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	24.8	0
Derivative Liability, Fair Value, Gross Liability	25.9	0
Equity Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	4,541.8	221.3
Derivative Liability, Fair Value, Gross Liability	4,794	245.4
TBA and forward settling securities [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	5	8.8
Derivative Liability, Fair Value, Gross Liability	2.1	4.9
TBA securities purchased [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	1.2
Derivative Liability, Fair Value, Gross Liability	(0.6)
Derivative Asset, Notional Amount	(721.5)
Derivative Liability, Notional Amount	(293.2)
TBA securities sold [Member] [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	3.2
Derivative Liability, Fair Value, Gross Liability	(1.5)
Derivative Asset, Notional Amount	(1,099.5)
Derivative Liability, Notional Amount	(812.7)
Forward settling securities purchased [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	0.5
Derivative Asset, Notional Amount	(614.3)
Forward settling securities sold [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	0.1
Derivative Liability, Notional Amount	(427.2)
Deposits and receivables from broker-dealers, clearing organizations and counterparties [Member]
Derivatives, Fair Value [Line Items]
Derivative, Fair Value, Net	(268.7)	(46.4)
Financial instruments owned [Member]
Derivatives, Fair Value [Line Items]
Derivative, Fair Value, Net	186.1	162.1
Payable to broker-dealers, clearing organizations and counterparties [Member]
Derivatives, Fair Value [Line Items]
Derivative, Fair Value, Net	0	4.8
Financial instrument sold, not yet purchased [Member]
Derivatives, Fair Value [Line Items]
Derivative, Fair Value, Net	193.4	317
Counterparty And Cash Collateral Netting Adjustment [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Amount Offset Against Collateral	(8,118.5)	(4,205.5)
Derivative Liability, Fair Value, Amount Offset Against Collateral	$ (8,317.6)	$ (3,879.2)

Financial Instruments with Of_5

Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk - Derivatives Volume (Details) number in Millions	Sep. 30, 2018	Sep. 30, 2017
Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk [Abstract]
Derivative, Number of Instruments Held	10.6	6.1

Financial Instruments with Of_6

Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk - Realized Gains/Losses on Derivative Contracts (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Commodity Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	$ 94	$ 47.3	$ 41.8
Foreign Exchange Forward [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	9.2	8.7	9.7
Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	1	(0.1)	0.8
TBA and forward settling securities [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	14.5	(2.5)	(14.4)
Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	$ 118.7	$ 53.4	$ 37.9

Receivables from customers, n_3

Receivables from customers, net and notes receivable, net - Allowance for Customer Receivables (Details) - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017
Receivables from customers and notes receivable, net [Abstract]
Allowance For Doubtful Accounts - Deposits with and Receivables from Broker-Dealers, Clearings Organizations, and Counterparties	$ 48	$ 47
Allowance for Doubtful Accounts Receivable	$ 10.2	$ 7.6

Receivables from customers, n_4

Receivables from customers, net and notes receivable, net - Bad Debt Expense and Recoveries (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for Doubtful Accounts		$ 3.1	$ 4.3	$ 4.4
Allowance for Doubtful Accounts Receivable, Period Increase (Decrease)		2.9	4.2	4.2
Provision for Other Losses		0.3	0.1
Bad debt on physical coal	$ 1	1	47	0
Allowance for Doubtful Accounts Receivable, Charge-offs		0.3	6.1	5.7
Allowance for Doubtful Accounts Receivable, Recoveries		0.1		0.2
Commercial Hedging [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for Doubtful Accounts Receivable, Period Increase (Decrease)		2.8	3.8	3.6
Allowance for Doubtful Accounts Receivable, Charge-offs				0.4
Physical Commodities Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for Doubtful Accounts Receivable, Period Increase (Decrease)			0.2	0.4
Clearing and Execution Services Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for Doubtful Accounts Receivable, Period Increase (Decrease)		$ 0.4	$ 0.3
Securities Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for Doubtful Accounts Receivable, Period Increase (Decrease)				$ 0.4

Receivables from customers, n_5

Receivables from customers, net and notes receivable, net - Allowance for Bad Debts Rollforward (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Allowance for Doubtful Accounts Receivable [Roll Forward]
Allowance for Doubtful Accounts - Customer and Notes Receivable	$ 54.6	$ 9.7	$ 11.2
Provision for bad debts	3.9	51	4.2
Allowance for Doubtful Accounts Receivable, Charge-offs	(0.3)	(6.1)	(5.7)
Allowance for Doubtful Accounts Receivable, Recoveries	0.1		0.2
Allowance for Doubtful Accounts - Customer and Notes Receivable	$ 58.2	$ 54.6	$ 9.7

Physical Commodities Inventor_3

Physical Commodities Inventory - Physical Commodities Inventory by CIP and Finished (Details) - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017
Inventory [Line Items]
Agricultural Related Inventory	$ 114.7	$ 65.1
Precious Metals Inventory at fair value	42.1	13.3
Precious Metals Inventory at cost	65.7	46.4
Inventory, Net	$ 222.5	$ 124.8

Physical Commodities Inventor_4

Physical Commodities Inventory - LCM Adjustments (Details) - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017
Physical Commodities Inventory [Abstract]
Inventory Adjustments	$ 0.4	$ 0.7

Property and Equipment, net (De

Property and Equipment, net (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Property, Plant and Equipment [Line Items]
Depreciation	$ 9.4	$ 7	$ 6.6
Furniture and Fixtures, Gross	8.7	7.2
Capitalized Computer Software, Gross	30.5	25.3
Machinery and Equipment, Gross	24.7	22.6
Leasehold Improvements, Gross	17	15.4
Property, Plant and Equipment, Gross	80.9	70.5
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	38.5	31.8
Property, Plant and Equipment, Net	$ 42.4	$ 38.7
Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Lives	3 years
Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Lives	10 years

Goodwill - Goodwill by Segment

Goodwill - Goodwill by Segment (Details) - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017
Goodwill [Line Items]
Goodwill	$ 48.4	$ 47.1
Commercial Hedging [Member]
Goodwill [Line Items]
Goodwill	30.3	30.7
Global Payments [Member]
Goodwill [Line Items]
Goodwill	8.9	6.3
Physical Commodities Segment [Member]
Goodwill [Line Items]
Goodwill	2.4	2.4
Securities Segment [Member]
Goodwill [Line Items]
Goodwill	$ 6.8	$ 7.7

Goodwill Goodwill Reconciliatio

Goodwill Goodwill Reconciliation (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Goodwill Disclosure [Abstract]
Goodwill, Translation and Purchase Accounting Adjustments	$ 1.3	$ 0
Goodwill, Acquired During Period	$ 2.6

Intangible Assets - Gross and N

Intangible Assets - Gross and Net Intangible Assets by Major Class (Details) - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Computer Software, Gross	$ 30.5	$ 25.3
Finite-Lived Intangible Assets, Gross	24.1	22.7
Finite-Lived Intangible Assets, Accumulated Amortization	(12.7)	(10.4)
Finite-Lived Intangible Assets, Net	11.4	12.3
Trade Names [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Trade Names, Gross	0	0
Finite-Lived Intangible Assets, Accumulated Amortization	0	0
Finite-Lived Intangible Assets, Net	0	0
Computer Software, Intangible Asset [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Computer Software, Gross	2.7	2.7
Finite-Lived Intangible Assets, Accumulated Amortization	(2.6)	(2.5)
Finite-Lived Intangible Assets, Net	0.1	0.2
Customer Relationships [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Customer Lists, Gross	21.4	20
Finite-Lived Intangible Assets, Accumulated Amortization	(10.1)	(7.9)
Finite-Lived Intangible Assets, Net	$ 11.3	$ 12.1

Intangible Assets - Finite-Live

Intangible Assets - Finite-Lived Intangible Assets Future Amortization Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Intangible Assets [Abstract]
Amortization of Intangible Assets	$ 2.3	$ 2.8	$ 1.6
Finite-Lived Intangible Assets, Amortization Expense, Maturity Schedule [Abstract]
Fiscal 2,019	2.5
Fiscal 2,020	2.2
Fiscal 2,021	2.2
Fiscal 2,022	1
Fiscal 2023 and thereafter	3.5
Finite-Lived Intangible Assets, Net	$ 11.4	$ 12.3

Intangible Assets Intangible As

Intangible Assets Intangible Asset Additions (Details) $ in Millions	12 Months Ended
	Sep. 30, 2018USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
Finite-lived Intangible Assets Acquired	$ 1.4

Credit Facilities - Number of C

Credit Facilities - Number of Credit Facilities (Details)	12 Months Ended
	Sep. 30, 2018USD ($)Rate	May 05, 2015USD ($)
Line of Credit Facility [Line Items]
Number of credit facilities	4
Line of Credit Facility, Maximum Borrowing Capacity | $	$ 150
HCO Syndicated line of credit facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage | Rate	0.625%
Line of Credit Facility, Interest Rate at Period End | Rate	5.17%
Line of Credit Facility, Maximum Borrowing Capacity | $	$ 262,000,000
HCO Syndicated line of credit facility [Member] | Eurodollar Rate [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate	3.00%
HCO Syndicated line of credit facility [Member] | Base Rate [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate	2.00%
INTL FCStone, Ltd [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity | $	$ 25,000,000
INTL FCStone, Ltd [Member] | Base Rate [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate	2.50%
INTL FCStone Financial Margin line of credit facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage | Rate	0.50%
Line of Credit Facility, Interest Rate at Period End | Rate	7.25%
Line of Credit Facility, Maximum Borrowing Capacity | $	$ 75,000,000	$ 75,000,000
INTL FCStone Financial Margin line of credit facility [Member] | Base Rate [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate	2.00%

Credit Facilities (Details)

Credit Facilities (Details) - USD ($)	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2013	Sep. 30, 2015	May 05, 2015	Apr. 15, 2015
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 150
Payables to lenders under loans	355,200,000	$ 230,200,000
Notes Payable to Bank	$ 1,200,000	2,000,000					$ 4,000,000
Debt Instrument, Interest Rate, Stated Percentage	8.50%
Debt Instrument, Call Feature, Redemption Price Percentage of Principal	100.00%
Payments of Debt Issuance Costs	$ 400,000	300,000	$ 2,100,000	$ 1,700,000
Senior Notes					$ 45,500,000
Debt and Capital Lease Obligations	$ 355,200,000	230,200,000
Write off of Deferred Debt Issuance Cost		1,000,000
Debt, Weighted Average Interest Rate	2.00%
HCO Syndicated line of credit facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	5.17%
Line of Credit Facility, Maximum Borrowing Capacity	$ 262,000,000
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.625%
Payables to lenders under loans	$ 208,200,000	150,000,000
INTL FCStone Financial Margin line of credit facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	7.25%
Line of Credit Facility, Maximum Borrowing Capacity	$ 75,000,000					$ 75,000,000
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.50%
Payables to lenders under loans	$ 0	0
INTL FCStone Financial Inc. Uncommitted Commodities Delivery Line [Domain]
Line of Credit Facility [Line Items]
Payables to lenders under loans	0	23,000,000
INTL FCStone Ltd. Uncommitted Line of Credit [Domain]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	20,000,000
Payables to lenders under loans	$ 0	0
Rabobank Uncommited Line of Credit [Domain]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	5.40%
Line of Credit Facility, Maximum Borrowing Capacity	$ 20,000,000
Letter of Credit Interest Rate	2.75%
Payables to lenders under loans	$ 3,800,000	0
FMS Sub-note commodity line of credit facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	4.77%
Line of Credit Facility, Maximum Borrowing Capacity	$ 232,500,000
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.38%
BMO Committed Credit Facility [Member] [Domain]
Line of Credit Facility [Line Items]
Payables to lenders under loans	$ 128,000,000	44,200,000
INTL FCStone, Ltd [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	25,000,000
Payables to lenders under loans	$ 0	0
INTL FCStone Financial Inc. Uncommitted Lines of Credit [Domain]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	2.88%
Payables to lenders under loans	$ 14,000,000	34,000,000
INTL FCStone Financial Inc. Uncommitted Sterne Legacy BNYM Line of Credit [Domain]
Line of Credit Facility [Line Items]
Payables to lenders under loans		0
INTL FCStone Financial Inc. Uncommitted Sterne BMO Line [Domain]
Line of Credit Facility [Line Items]
Payables to lenders under loans	0	$ 11,000,000
Main line of credit facilities [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	594,500,000
Line of Credit Facility, Current Borrowing Capacity	$ 362,000,000
Base Rate [Member] | HCO Syndicated line of credit facility [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate	2.00%
Base Rate [Member] | INTL FCStone Financial Margin line of credit facility [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate	2.00%
Base Rate [Member] | INTL FCStone Financial Inc. Uncommitted Commodities Delivery Line [Domain]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate	2.50%
Base Rate [Member] | Sterne Agee [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate	2.00%
Base Rate [Member] | Rabobank Uncommited Line of Credit [Domain]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate	2.00%
Base Rate [Member] | INTL FCStone, Ltd [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate	2.50%
Cost of Funds Rate [Domain] | Rabobank Uncommited Line of Credit [Domain]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate	3.00%

Commitments and Contingencies -

Commitments and Contingencies - Contingencies and Litigation (Details) $ in Millions	3 Months Ended
	Dec. 31, 2017USD ($)
Commitments and Contingencies [Abstract]
Excess segregated funds returned	$ 15.5

Commitments and Contingencies_2

Commitments and Contingencies - Operating Leases (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Operating Leases [Abstract]
Operating Leases, Rent Expense	$ 12	$ 11.3	$ 9.9
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
Operating Leases, Future Minimum Payments Due, Next Twelve Months	10.1
Operating Leases, Future Minimum Payments, Due in Two Years	9.3
Operating Leases, Future Minimum Payments, Due in Three Years	8.1
Operating Leases, Future Minimum Payments, Due in Four Years	5.8
Operating Leases, Future Minimum Payments, Due in Five Years	4.5
Operating Leases, Future Minimum Payments, Due Thereafter	5.6
Operating Leases, Future Minimum Payments Due	$ 43.4

Commitments and Contingencies_3

Commitments and Contingencies - Purchase Obligations (Details) - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017
Commitments and Contingencies Disclosure [Abstract]
Purchase Obligation, Due in Next Twelve Months	$ 1,204.7
Purchase Obligation, Due in Second and Third Year	1.7
Purchase Obligation, Due in Fourth and Fifth Year	1.8
Purchase Obligation, Due after Fifth Year		$ 2
Other Commitment, Due in Next Twelve Months	$ 1,406

Commitments and Contingencies_4

Commitments and Contingencies - Self-Insurance (Details) $ in Millions	Sep. 30, 2018USD ($)
Commitments and Contingencies [Abstract]
Self Insurance Reserve	$ 0.8

Regulatory Requirements and S_3

Regulatory Requirements and Subsidiary Dividend Restrictions - Minimum net capital (Details)	Sep. 30, 2017USD ($)
Capital and Other Regulatory Requirements [Abstract]
Minimum Net Capital Required for Broker-Dealer Subsidiary	$ 1,000,000
Minimum Net Capital Required for Entity	$ 0.08

Regulatory Requirements and S_4

Regulatory Requirements and Subsidiary Dividend Restrictions - Regulatory Capital Requirements (Details) - USD ($)	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Minimum Net Capital Required for Entity		$ 0.08
Cash Held at Banks and Money Market Funds - Segregated	$ 765,400,000	$ 464,300,000
INTL FCStone Financial [Member]
Net Capital	167,700,000
Cash and Securities Segregated under Commodity Exchange Act Regulation	2,637,000,000
Secured funds	148,900,000
Minimum Net Capital Required for Entity	101,400,000
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	2,579,700,000
Secured Funds Required Under Commodity Exchange Act	132,800,000
Cash Reserve Deposit Required and Made			$ 6,400,000
Cash Held at Banks and Money Market Funds - Segregated	300,000
Sterne Agee Clearing, Inc. [Member]
Net Capital	0
Minimum Net Capital Required for Entity	0
Sterne Agee Financial Services, Inc. [Member]
Net Capital	4,600,000
Minimum Net Capital Required for Entity	400,000
INTL FCStone, Ltd [Member]
Cash and Securities Segregated under Commodity Exchange Act Regulation	187,300,000
Net Capital under Commodity Exchange Act Computation	193,100,000
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	182,100,000
Required Net Capital under Commodity Exchange Act	95,900,000
INTL FCStone Europe [Member]
Net Capital under Commodity Exchange Act Computation	193,000,000
Required Net Capital under Commodity Exchange Act	95,900,000
INTL FCStone DTVM Ltda [Member]
Net Capital	11,200,000
Capital Required for Capital Adequacy	2,100,000
Gainvest S.A. Sociedad Gerente de FCI - Comision Nacional de Valores [Member]
Net Capital	4,200,000
Net Capital under Commodity Exchange Act Computation	1,200,000
Required Net Capital under Commodity Exchange Act	100,000
Capital Required for Capital Adequacy	100,000
INTL CIBSA S.A. - Comision Nacional de Valores [Member]
Net Capital	4,400,000
Net Capital under Commodity Exchange Act Computation	0
Required Net Capital under Commodity Exchange Act	0
Capital Required for Capital Adequacy	$ 500,000

Commodity and Other Repurchas_4

Commodity and Other Repurchase Agreements (Details) - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017
Securities sold under agreements to repurchase	$ 1,936.7	$ 1,393.1
Fair Value of Securities Received as Collateral that Can be Resold or Repledged	1,294.8	631.7
Fair Value of Securities Received as Collateral that Have Been Resold or Repledged	473.9	306.9
Financial Instruments Owned and Pledged as Collateral, Amount Eligible to be Repledged by Counterparty	123	19.4
Securities Loaned, Fair Value of Collateral	267.9	108.4
Financial Instruments Owned and Pledged as Collateral, Amount Not Eligible to be Repledged by Counterparty	1,481.1	1,306.4
Securities Loaned	277.9	111.1
Collateralized Financings	2,214.6	1,504.2
Sales Repurchase Agreements	1.9	0.8
Securities Sold under Agreements to Repurchase, Fair Value of Collateral	123	19.4
Trading Securities Pledged as Collateral	27.1	12.7
Pledged Financial Instruments, Not Separately Reported, Securities for Repurchase Agreements	369.8	100.2
Maturity Overnight [Member]
Securities sold under agreements to repurchase	934.9	640.2
Securities Loaned	277.9	111.1
Collateralized Financings	1,212.8	751.3
Maturity Less than 30 Days [Member]
Securities sold under agreements to repurchase	661.3	432.9
Securities Loaned	0	0
Collateralized Financings	661.3	432.9
Maturity 30 to 90 Days [Member]
Securities sold under agreements to repurchase	340.5	320
Securities Loaned	0	0
Collateralized Financings	340.5	320
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Securities sold under agreements to repurchase		1,017.1
Asset-backed Securities [Member]
Securities sold under agreements to repurchase	50	36.4
US Government Debt Securities [Member]
Securities sold under agreements to repurchase	39.6	7
US Government Agencies Debt Securities [Member]
Securities sold under agreements to repurchase	461.7	332.6
Equity Securities [Member]
Securities Loaned	$ 277.9	$ 111.1

Share-Based Compensation - Shar

Share-Based Compensation - Share-based Compensation Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Allocated Share-based Compensation Expense	$ 6.6	$ 6.3	$ 5.1

Share-Based Compensation - Stoc

Share-Based Compensation - Stock Option Plan (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	1,000,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	588,020	652,494
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 9.79	$ 8.67	$ 6.40
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Stock Options	$ 3
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition	3 years 1 month 17 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Total Intrinsic Value	$ 2.1	$ 2.6	$ 1.9

Share-Based Compensation - St_2

Share-Based Compensation - Stock Option Plan Fair Value Weighted-Average Assumptions (Details)	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate	30.00%	31.00%	28.00%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate	0.00%	0.00%	0.00%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate	1.23%	0.99%	0.83%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term	3 years 22 days	3 years 29 days	3 years 22 days

Share-Based Compensation - Sh_2

Share-Based Compensation - Share-Based Compensation Table (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	1,000,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	652,494
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	881,403
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	(79,800)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Period Increase (Decrease)	79,800
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period	(110,423)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period	13,324
Share-based Compensation Arrangement by Share-based Payment Award, Options, Other Increases (Decreases) in Period	(13,324)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Expirations in Period	(2,002)
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	588,020	652,494
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	835,454	881,403
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number	314,366
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price	$ 29.27	$ 27.31
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price	44.17
Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price	23.79
Share-based Compensation Arrangements by Share-based Payment Award, Options, Forfeitures in Period, Weighted Average Exercise Price	33.19
Share-based Compensation Arrangements by Share-based Payment Award, Options, Expirations in Period, Weighted Average Exercise Price	32.60
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price	27.16
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Grant Date Fair Value	11.93	11.55
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value	9.79	$ 8.67	$ 6.40
Share-based Compensation Arrangement by Share-based Payment Award, Options, Excrecises in Period, Weighted Average Grant Date Fair Value	7.98
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeited in Period, Weighted Average Grant Date Fair Value	7.14
Share-based Compensation Arrangement by Share-based Payment Award, Options, Expired in Period, Weighted Average Grant Date Fair Value	6.78
Share-based Compensation Arrangement by Share-based Payment Award, Options, Excercisable, Weighted Average Grant Date Fair Value	$ 11.68
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term		3 years 4 days	3 years 6 months 26 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term		2 years 9 months 22 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value	$ 15.9	$ 9.8
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value	6.7
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Stock Options	$ 3
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition	3 years 1 month 17 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Total Intrinsic Value	$ 2.1	$ 2.6	$ 1.9

Share-Based Compensation - Opti

Share-Based Compensation - Options by Exercise Price (Details)	12 Months Ended
	Sep. 30, 2018$ / sharesshares
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of Outstanding Options | shares	835,454
Weighted Average Exercise Price	$ 29.27
Weighted Average Remaining Term (in years)	3 years 4 days
$0 - $5,00 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Range, Lower Range Limit	$ 0
Exercise Price Range, Upper Range Limit	$ 5
Number of Outstanding Options | shares	0
$5.00 - $10.00 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Range, Lower Range Limit	$ 5
Exercise Price Range, Upper Range Limit	$ 10
Number of Outstanding Options | shares	0
$10.00 - $15.00 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Range, Lower Range Limit	$ 10
Exercise Price Range, Upper Range Limit	$ 15
Number of Outstanding Options | shares	0
$15.00 - $20.00 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Range, Lower Range Limit	$ 15
Exercise Price Range, Upper Range Limit	$ 20
Number of Outstanding Options | shares	0
$20.00 - $25.00 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Range, Lower Range Limit	$ 20
Exercise Price Range, Upper Range Limit	$ 25
Number of Outstanding Options | shares	28,668
Weighted Average Exercise Price	$ 20.54
Weighted Average Remaining Term (in years)	3 months 7 days
$25.00 - $30.00 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Range, Lower Range Limit	$ 25
Exercise Price Range, Upper Range Limit	$ 30
Number of Outstanding Options | shares	580,000
Weighted Average Exercise Price	$ 25.91
Weighted Average Remaining Term (in years)	3 years 4 months 13 days
$30.00 - $35.00 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Range, Lower Range Limit	$ 30
Exercise Price Range, Upper Range Limit	$ 35
Number of Outstanding Options | shares	49,656
Weighted Average Exercise Price	$ 31.37
Weighted Average Remaining Term (in years)	1 year 3 months 11 days
$35.00 - $40.00 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Range, Lower Range Limit	$ 35
Exercise Price Range, Upper Range Limit	$ 40
Number of Outstanding Options | shares	100,330
Weighted Average Exercise Price	$ 38.77
Weighted Average Remaining Term (in years)	2 years 3 months 7 days
$40.00 - $45.00 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Range, Lower Range Limit	$ 40
Exercise Price Range, Upper Range Limit	$ 45
Number of Outstanding Options | shares	74,800
$45.00 - $50.00 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Range, Lower Range Limit	$ 45
Exercise Price Range, Upper Range Limit	$ 50
Number of Outstanding Options | shares	0
$50.00 - $55.00 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Range, Lower Range Limit	$ 50
Exercise Price Range, Upper Range Limit	$ 55
Number of Outstanding Options | shares	2,000

Share-Based Compensation - Rest

Share-Based Compensation - Restricted Stock Plan (Details) $ in Millions	12 Months Ended
	Sep. 30, 2018USD ($)shares
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period	1,500,000
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted	1,377,278
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized | $	$ 6.8
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition - Restricted Stock	1 year 1 month 24 days

Share-Based Compensation - Re_2

Share-Based Compensation - Restricted Stock Plan Table (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted	1,377,278
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period	1,500,000
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward]
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding, Number	1,459,976
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Period Increase (Decrease)	(85,404)
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Forfeitures	2,706
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding, Number	1,377,278	1,459,976
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	354,474
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	85,404
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period	(162,544)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period	(2,706)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	274,628	354,474
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value	$ 33.34
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	44.86
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value	31.14
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value	36.24
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value	$ 38.20	$ 33.34
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Outstanding, Weighted Average Remaining Contractual Terms	1 year 1 month 24 days	1 year 3 months 4 days
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Outstanding	$ 13.3	$ 13.6
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized	$ 6.8
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition - Restricted Stock	1 year 1 month 24 days

Retirement Plans Retirement Pla

Retirement Plans Retirement Plans - Defined Contribution Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Defined Contribution Plan Disclosure [Line Items]
Defined Contribution Plan, Employer Discretionary Contribution Amount	$ 6.8	$ 6.1	$ 5.3
UK Plan [Member]
Defined Contribution Plan Disclosure [Line Items]
Defined Contribution Plan, Employers Matching Contribution, Annual Vesting Percentage	100.00%
UK Plan [Member] | Maximum [Member]
Defined Contribution Plan Disclosure [Line Items]
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	10.00%
401k Plan [Member]
Defined Contribution Plan Disclosure [Line Items]
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	62.50%
Defined Contribution Plan, Employers Matching Contribution, Annual Vesting Percentage	8.00%
Defined Contribution Plan, Employers Matching Contribution, Annual Vesting Percentage, Two to Three Years	33.00%
Defined Contribution Plan, Employers Matching Contribution, Annual Vesting Percentage, Three to Four Years	66.00%
Defined Contribution Plan, Employers Matching Contribution, Annual Vesting Percentage, All Years	100.00%
401k Plan [Member] | Maximum [Member]
Defined Contribution Plan Disclosure [Line Items]
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent	80.00%
401k Plan [Member] | Minimum [Member]
Defined Contribution Plan Disclosure [Line Items]
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent	1.00%

Retirement Plans Retirement P_2

Retirement Plans Retirement Plans - Defined Benefit Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	$ 0.2		$ 0.2
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets	5.00%
Defined Benefit Plan, Expected Future Benefit Payment, Year Three	$ 2
Defined Benefit Plan, Expected Future Benefit Payment, Year Four	2
Defined Benefit Plan, Expected Future Benefit Payment, Year Five	2
Defined Benefit Plan, Expected Future Benefit Payment, Five Fiscal Years Thereafter	9.7
Defined Benefit Plan, Plan Assets, Contributions by Employer	1	$ 2
Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year	2.1
Defined Benefit Plan, Expected Future Benefit Payment, Year Two	$ 2
Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Actual Plan Asset Allocations	20.00%
Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Actual Plan Asset Allocations	80.00%
Nonqualified Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	$ 0.1
Defined Benefit Plan, Pension Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Projected Benefit Obligation	1.6	1.7
Qualified Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	35.6	36.3
Defined Benefit Plan, Benefit Obligation	$ 32.5	$ 34.7
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	4.20%	3.75%

Other Expenses - Other Expenses

Other Expenses - Other Expenses Breakout (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Other Expenses [Abstract]
Accretion Expense	$ 0	$ 0.1	$ 0.4
General Insurance Expense	2.6	2.7	2.1
Advertising Expense	6.2	4	5.1
Supplies and Postage Expense	1.7	2.1	1.2
Clearance Fees	2.5	2.6	1.3
Taxes, Miscellaneous	4.9	4.6	4.3
Other Expenses	8.4	9.8	7.9
Operating Costs and Expenses	$ 26.3	$ 25.9	$ 22.3

Bad Debt on Physical Coal (Deta

Bad Debt on Physical Coal (Details) - USD ($) $ in Millions	3 Months Ended				12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Bad Debt on Physical Coal [Abstract]
Bad debt on physical coal	$ 0	$ 0	$ 0	$ 1	$ 1	$ 47	$ 0

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Operating Loss Carryforwards [Line Items]
Deferred Tax Liabilities, Other	$ 0.4				$ 0				$ 0.4	$ 0
Income tax expense	4.8	$ 8.9	$ 6.8	$ 25.5	1.1	$ 2.3	$ 3.3	$ 2.1	46	8.8	$ 18
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized (Gain) Loss Arising During Period, Tax									0.1	1	0.2
Adjustments to Additional Paid in Capital, Income Tax Benefit from Share-based Compensation									0	0.1	0.8
Other Comprehensive Income (Loss), Tax									46.1	9.9	17.4
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense									0
Operating Loss Carryforwards	9.4				30.1				9.4	30.1
Deferred Tax Assets, Operating Loss Carryforwards, Domestic	0				21.9				0	21.9
Deferred Tax Assets, Net of Valuation Allowance, Operating Loss Carryforwards, State and Local	5.7								5.7
Deferred Tax Assets, Valuation Allowance	3.5				$ 4				3.5	4
Valuation Allowance, Deferred Tax Asset, Change in Amount									0.5
Income (Loss) from Continuing Operations before Income Taxes, Domestic									(3.7)	$ (20.5)	$ (9.7)
Deferred Tax Liabilities, Gross	5								5
Undistributed Earnings of Foreign Subsidiaries	354.7								354.7
UNITED STATES
Operating Loss Carryforwards [Line Items]
Deferred Tax Liabilities, Other	$ 2.5								$ 2.5

Income Taxes - Current and Defe

Income Taxes - Current and Deferred Taxes (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Income Tax Disclosure [Abstract]
Current Federal Tax Expense (Benefit)									$ 0.8	$ 0.7	$ 1.3
Current State and Local Tax Expense (Benefit)									0.5	1.2	0.8
Current Foreign Tax Expense (Benefit)									22.4	16.7	16.8
Current Income Tax Expense (Benefit)									23.7	18.6	18.9
Deferred Income Tax Expense (Benefit)									22.3	(9.8)	(0.8)
Other Tax Expense (Benefit)									0	0	(0.1)
Income tax expense	$ 4.8	$ 8.9	$ 6.8	$ 25.5	$ 1.1	$ 2.3	$ 3.3	$ 2.1	$ 46	$ 8.8	$ 18

Income Taxes - US and Internati

Income Taxes - US and International Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Income Tax Disclosure [Abstract]
Income (Loss) from Continuing Operations before Income Taxes, Domestic	$ 9.9	$ (13.9)	$ 4.8
Income (Loss) from Continuing Operations before Income Taxes, Foreign	91.6	29.1	67.9
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	$ 101.5	$ 15.2	$ 72.7

Income Taxes - Effective Rate R

Income Taxes - Effective Rate Reconciliation (Details)	12 Months Ended
	Sep. 30, 2018Rate	Sep. 30, 2017Rate	Sep. 30, 2016Rate
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate	24.53%	35.00%	35.00%
Effective Income Tax Rate Reconciliation, State and Local Income Taxes	0.80%	(2.60%)	1.30%
Effective Income Tax Rate Reconciliation, Foreign Income Tax Rate Differential	(0.80%)	11.50%	(11.00%)
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Meals and Entertainment	(0.20%)	(3.60%)	(0.80%)
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Other	2.10%	8.10%	1.90%
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent	0.00%	0.00%	(3.00%)
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Percent	8.50%	0.00%	0.00%
Effective Income Tax Rate Reconciliation, Repatriation of Foreign Earnings, Percent	11.00%	0.00%	0.00%
Effective Income Tax Rate Reconciliation, Deductions, Other	(0.20%)	(0.60%)	(0.30%)
Effective Income Tax Rate, Continuing Operations	45.30%	57.70%	25.00%
Foreign Tax Authority [Member]
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance	(0.80%)	(1.40%)	(0.30%)
State and Local Jurisdiction [Member]
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance	0.00%	4.10%	0.00%

Income Taxes - Deferred Tax Ass

Income Taxes - Deferred Tax Assets and Liabilites (Details) - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards, Foreign	$ 4.2	$ 5.6
Deferred Tax Assets, Tax Credit Carryforwards, Foreign	6.5	0
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Share-based Compensation Cost	2.8	3.7
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Pensions	0	0.1
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Employee Compensation	1.4	2
Deferred Tax Assets, Operating Loss Carryforwards, State and Local	8.7	6.6
Deferred Tax Assets, Operating Loss Carryforwards, Domestic	0	21.9
Deferred Tax Assets, Intangible Assets	1.8	6.1
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Allowance for Doubtful Accounts	1.5	1.4
Deferred Tax Assets, Tax Credit Carryforwards, Alternative Minimum Tax	0	1.6
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits	3.4	3.6
Deferred Tax Assets, Other	0.9	1.9
Deferred Tax Assets, Gross	31.2	54.5
Deferred Tax Assets, Valuation Allowance	(3.5)	(4)
Deferred Tax Assets, Net of Valuation Allowance	27.7	50.5
Deferred Tax Liabilities, Unrealized Gains on Trading Securities	2.6	3.2
Deferred Tax Liabilities, Prepaid Expenses	1.8	2.5
Deferred Tax Liabilities, Property, Plant and Equipment	3.1	2.2
Deferred Tax Liabilities, Pension Liability	0.4	0
Deferred Tax Liabilities, Gross	7.9	7.9
Deferred tax assets, Net	19.8	$ 42.6
SINGAPORE
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards, Foreign	2.9
UNITED STATES
Operating Loss Carryforwards [Line Items]
Deferred Tax Liabilities, Pension Liability	2.5
Tax Period [Domain]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Tax Credit Carryforwards, Foreign	$ 6.5

Income Taxes - FIN 48 Analysis

Income Taxes - FIN 48 Analysis (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Income Tax Disclosure [Abstract]
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense	$ 0
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance beginning of year	0.1	$ 0.1	$ 0
Gross increases for tax positions related to prior years	0	0	0.1
Balance end of year	$ 0.1	$ 0.1	$ 0.1

Income Taxes Income Taxes - Tax

Income Taxes Income Taxes - Tax Reform (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Subsequent Event [Line Items]
Effective Income Tax Rate Reconciliation, Repatriation of Foreign Earnings, Amount		$ 11.2
Undistributed Earnings of Foreign Subsidiaries		$ 354.7
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate		24.53%	35.00%	35.00%
Income Tax Expense (Benefit), Continuing Operations, Adjustment of Deferred Tax (Asset) Liability		$ 8.6
Scenario, Forecast [Member]
Subsequent Event [Line Items]
Foreign Earnings Repatriated	$ 13

Acquisitions PayCommerce Financ

Acquisitions PayCommerce Financial Solutions Acquisition (Details) $ in Millions	12 Months Ended
	Sep. 30, 2018USD ($)
Business Acquisition [Line Items]
Goodwill, Acquired During Period	$ 2.6
PayCommerce [Member] [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred	3.8
Business Combination, Acquired Receivable, Fair Value	0.7
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment	0.8
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Financial Assets	0.5
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities	2.2
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles	$ 1.3
Finite-Lived Intangible Asset, Useful Life	5 years
Goodwill, Acquired During Period	$ 2.6

Acquisitions ICAP (Details)

Acquisitions ICAP (Details) $ in Millions	12 Months Ended
	Sep. 30, 2018USD ($)
Business Acquisition [Line Items]
Finite-lived Intangible Assets Acquired	$ 1.4
ICAP [Member] [Member]
Business Acquisition [Line Items]
Finite-lived Intangible Assets Acquired	$ 6

Sterne Agee (Details)

Sterne Agee (Details) - Sterne Agee [Member] $ in Millions	12 Months Ended
	Sep. 30, 2016USD ($)
Business Acquisition [Line Items]
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual	$ 8.6
Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual	0.1
Business Combination, Consideration Transferred	45
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents	24.9
Business Combination, Acquired Receivable, Fair Value	151.6
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Assets Noncurrent	5.7
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Prepaid Expense and Other Assets	4.8
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities	136
Business Combination, Bargain Purchase, Gain Recognized, Amount	$ 6.2

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, net	$ (33.1)	$ (24.5)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax	(9)	(1.4)	$ (7.4)
Other Comprehensive (Income) Loss, Defined Benefit Plan, before Reclassification Adjustment, after Tax	(0.3)	(1.2)	0.2
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax	0.1	0.4	0.5
Other Comprehensive Income (Loss), Net of Tax	(8.6)	0.1	(7.1)
Accumulated Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, net	(30.5)	(21.5)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax	(9)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, before Tax	0
Other Comprehensive Income (Loss), Net of Tax	(9)
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, net	(2.6)	(3)
Other Comprehensive (Income) Loss, Defined Benefit Plan, before Reclassification Adjustment, after Tax	0.3
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax	0.1
Other Comprehensive Income (Loss), Net of Tax	0.4
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, net	(33.1)	(24.5)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(8.7)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0.1
Other Comprehensive Income (Loss), Net of Tax	$ (8.6)	$ 0.1	$ (7.1)

Quarterly Financial Informati_3

Quarterly Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 6,078.8	$ 7,118.3	$ 6,507	$ 7,918.6	$ 12,382.5	$ 5,505.9	$ 5,460.8	$ 6,074.4	$ 27,622.7	$ 29,423.6	$ 14,754.9
Cost of sales of physical commodities	5,835.6	6,858.5	6,246.8	7,706	12,177.4	5,308.3	5,265	5,888.9	26,646.9	28,639.6	14,083.9
Operating revenues	243.2	259.8	260.2	212.6	205.1	197.6	195.8	185.5	975.8	784	671
Transaction-based clearing expenses	43.1	49	50.7	36.9	35.1	33.9	33.7	33.6	179.7	136.3	129.9
Introducing broker commissions	32.4	34.1	36.2	31.1	26.9	29.2	28.2	28.7	133.8	113	68.9
Interest expense	25.3	22.1	19	14.3	12	11.2	10	8.9	80.7	42.1	28.3
Net operating revenues	142.4	154.6	154.3	130.3	131.1	123.3	123.9	114.3	581.6	492.6	443.9
Compensation and benefits	85.4	86.9	88.2	77.2	73	75.5	76.6	70.6	337.7	295.7	263.9
Bad debts	1.2	1.6	0.2	0.1	0.4	0.1	1.3	2.5	3.1	4.3	4.4
Bad debt on physical coal	0	0	0	1					1	47	0
Other	35.3	35.2	36.4	33.4	33.2	32.7	31.7	32.8	26.3	25.9	22.3
Total compensation and other expenses	121.9	123.7	124.8	111.7	153.6	108.3	109.6	105.9	482.1	477.4	377.4
Income before tax	20.5	32.9	29.5	18.6	(22.5)	15	14.3	8.4	101.5	15.2	72.7
Income tax expense	4.8	8.9	6.8	25.5	1.1	2.3	3.3	2.1	46	8.8	18
Net income	$ 15.7	$ 24	$ 22.7	$ (6.9)	$ (23.6)	$ 12.7	$ 11	$ 6.3	$ 55.5	$ 6.4	$ 54.7
Net basic earnings per share	$ 0.83	$ 1.27	$ 1.20	$ (0.37)	$ (1.27)	$ 0.67	$ 0.58	$ 0.34
Net diluted earnings per share	$ 0.81	$ 1.25	$ 1.18	$ (0.37)	$ (1.27)	$ 0.66	$ 0.58	$ 0.34

Segment and Geographic Inform_3

Segment and Geographic Information (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting Information [Line Items]
Revenues	$ 6,078.8	$ 7,118.3	$ 6,507	$ 7,918.6	$ 12,382.5	$ 5,505.9	$ 5,460.8	$ 6,074.4	$ 27,622.7	$ 29,423.6	$ 14,754.9
Operating revenues	243.2	259.8	260.2	212.6	205.1	197.6	195.8	185.5	975.8	784	671
Revenues, Net of Interest Expense	142.4	154.6	154.3	130.3	131.1	123.3	123.9	114.3	581.6	492.6	443.9
Net Segment Contribution									432.4	387	347
Segment Income									261.9	169	206
Costs not allocated to operating segments									162.4	153.8	139.5
Other gains									2	0	6.2
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	20.5	$ 32.9	$ 29.5	$ 18.6	(22.5)	$ 15	$ 14.3	$ 8.4	101.5	15.2	72.7
Assets	7,824.7				6,243.4				7,824.7	6,243.4	5,950.3
Commercial Hedging [Member]
Segment Reporting Information [Line Items]
Revenues									286.7	244.6	236.1
Operating revenues									286.7	244.6	236.1
Revenues, Net of Interest Expense									226.4	194.3	188.2
Net Segment Contribution									164.7	141.8	134.4
Segment Income									96.4	72.8	68.7
Assets	1,935.7				1,650.3				1,935.7	1,650.3	1,637.5
Global Payments [Member]
Segment Reporting Information [Line Items]
Revenues									99.2	89.2	73.2
Operating revenues									99.2	89.2	73.2
Revenues, Net of Interest Expense									93.5	80.6	65.3
Net Segment Contribution									75	64.4	52.2
Segment Income									59.8	50.6	39.8
Assets	206.6				199.5				206.6	199.5	191.4
Securities Segment [Member]
Segment Reporting Information [Line Items]
Revenues									196.2	151.7	175.2
Operating revenues									196.2	151.7	175.2
Revenues, Net of Interest Expense									94.6	94.6	121.9
Net Segment Contribution									69.1	75.6	97.5
Segment Income									40.8	46.6	69.4
Assets	3,058.2				2,101.7				3,058.2	2,101.7	2,130.7
Physical Commodities Segment [Member]
Segment Reporting Information [Line Items]
Revenues									26,703.8	28,684.4	14,120.5
Operating revenues									56.9	44.8	36.6
Revenues, Net of Interest Expense									44.8	37.3	31.5
Net Segment Contribution									31.8	27.2	23.4
Segment Income									16.6	(31.4)	13.3
Assets	413.7				339.5				413.7	339.5	258
Clearing and Execution Services Segment [Member]
Segment Reporting Information [Line Items]
Revenues									332.4	259.8	151.1
Operating revenues									332.4	259.8	151.1
Revenues, Net of Interest Expense									122.6	102.2	48.8
Net Segment Contribution									91.8	78	39.5
Segment Income									48.3	30.4	14.8
Assets	2,109.9				1,818.9				2,109.9	1,818.9	1,617.4
Corporate [Member]
Segment Reporting Information [Line Items]
Revenues									4.4	(6.1)	(1.2)
Operating revenues									4.4	(6.1)	(1.2)
Revenues, Net of Interest Expense									(0.3)	(16.4)	(11.8)
Assets	$ 100.6				$ 133.5				$ 100.6	$ 133.5	$ 115.3

Segment and Geographic Inform_4

Segment and Geographic Information - Total Revenues by Geographic Location (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Revenues	$ 6,078.8	$ 7,118.3	$ 6,507	$ 7,918.6	$ 12,382.5	$ 5,505.9	$ 5,460.8	$ 6,074.4	$ 27,622.7	$ 29,423.6	$ 14,754.9
Gross Profit	243.2	$ 259.8	$ 260.2	$ 212.6	205.1	$ 197.6	$ 195.8	$ 185.5	975.8	784	671
Long-Lived Assets	42.4				38.7				42.4	38.7	29.4
UNITED STATES
Revenues									1,587.6	1,168	817.1
Gross Profit									695.3	529.4	457
Long-Lived Assets	33				29.7				33	29.7	23.3
Europe [Member]
Revenues									189.6	166.9	463.5
Gross Profit									189	166.9	120.2
Long-Lived Assets	6.8				7.3				6.8	7.3	4.8
South America [Member]
Revenues									59.5	53.9	64.8
Gross Profit									58	54	64.8
Long-Lived Assets	1.4				1.5				1.4	1.5	1.2
Asia [Member]
Revenues									25,781.4	28,030.3	13,405.1
Gross Profit									28.9	29.2	24.6
Long-Lived Assets	$ 1.2				$ 0.2				1.2	0.2	0.1
Other (geographic location) [Member]
Revenues									4.6	4.5	4.4
Gross Profit									$ 4.6	$ 4.5	$ 4.4

Condensed Parent Only Financi_2

Condensed Parent Only Financial Statements - Balance Sheet (Details) - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Cash and cash equivalents	$ 342.3	$ 314.9	$ 316.2	$ 268.1
Income taxes receivable	0.3	0.4
Financial instruments owned, at fair value	2,054.8	1,731.8
Deferred tax assets, Net	19.8	42.6
Property and equipment, net	42.4	38.7
Total assets	7,824.7	6,243.4	5,950.3
Liabilities:
Accounts payable and other accrued liabilities	145.4	135.6
Payables to Customers	3,639.6	3,072.9
Payables to lenders under loans	355.2	230.2
Financial Instruments Sold, Not yet Purchased, at Fair Value	866.5	717.6
Total liabilities	7,319.4	5,793.5
INTL FCStone Inc. (Parent Company Only) stockholders’ equity:
Common stock, $0.01 par value. Authorized 30,000,000 shares; 21,030,497 issued and 18,908,540 outstanding at September 30, 2018 and 20,855,243 issued and 18,733,286 outstanding at September 30, 2017	0.2	0.2
Common stock in treasury, at cost - 2,121,957 shares at September 30, 2018 and 2017	(46.3)	(46.3)
Additional Paid in Capital	267.5	259
Retained earnings	317	261.5
Total INTL FCStone Inc. (Parent Company Only) stockholders’ equity	505.3	449.9
Total liabilities and stockholders' equity	7,824.7	6,243.4
Parent Company [Member]
Cash and cash equivalents	1.8	2	1.3	$ 2.5
Receivables from subsidiaries	23.3	3.8
Notes receivable, net	1.8	4.8
Income taxes receivable	14.9	8.6
Investment in subsidiaries	318	312.3
Financial instruments owned, at fair value	4.4	0
Deferred tax assets, Net	8.8	26.5
Property and equipment, net	25.9	24.8
Other assets	7.6	7.6
Total assets	406.5	390.4
Liabilities:
Accounts payable and other accrued liabilities	23	19.8
Payables to Customers	1.7	2.1
Payables to lenders under loans	209.4	152
Payable to subsidiaries, net	0	49.4
Financial Instruments Sold, Not yet Purchased, at Fair Value	59.3	25.3
Total liabilities	293.4	248.6
INTL FCStone Inc. (Parent Company Only) stockholders’ equity:
Preferred stock, $.01 par value. Authorized 1,000,000 shares; no shares issued or outstanding	0	0
Common stock, $0.01 par value. Authorized 30,000,000 shares; 21,030,497 issued and 18,908,540 outstanding at September 30, 2018 and 20,855,243 issued and 18,733,286 outstanding at September 30, 2017	0.2	0.2
Common stock in treasury, at cost - 2,121,957 shares at September 30, 2018 and 2017	(46.3)	(46.3)
Additional Paid in Capital	267.5	259
Retained earnings	(108.3)	(71.1)
Total INTL FCStone Inc. (Parent Company Only) stockholders’ equity	113.1	141.8
Total liabilities and stockholders' equity	$ 406.5	390.4
Adjustment to Investment in Subs for Equity Method Accounting		$ 425.3	$ 332.6

Condensed Parent Only Financi_3

Condensed Parent Only Financial Statements - Balance Sheet (Parentheticals) (Details) - $ / shares	Sep. 30, 2018	Sep. 30, 2017
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Preferred stock - par value	$ 0.01	$ 0.01
Preferred stock - authorized	1,000,000	1,000,000
Preferred stock - issued	0	0
Preferred stock - outstanding	0	0
Common stock - par value	$ 0.01	$ 0.01
Common stock - authorized	30,000,000	30,000,000
Common stock - issued	21,030,497	20,855,243
Common stock - outstanding	18,908,540	18,733,286
Treasury stock - shares	2,121,957	2,121,957

Condensed Parent Only Financi_4

Condensed Parent Only Financial Statements - Income Statement (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Condensed Financial Statements, Captions [Line Items]
Trading gains, net									$ 389.1	$ 332.2	$ 321.2
Consulting fees									356.8	283.4	224.3
Interest income									123.3	69.7	55.2
Dividend income from subsidiaries									41.9	52.7	31
Operating revenues	$ 243.2	$ 259.8	$ 260.2	$ 212.6	$ 205.1	$ 197.6	$ 195.8	$ 185.5	975.8	784	671
Interest expense	25.3	22.1	19	14.3	12	11.2	10	8.9	80.7	42.1	28.3
Net operating revenues	142.4	154.6	154.3	130.3	131.1	123.3	123.9	114.3	581.6	492.6	443.9
Non-interest expenses:
Compensation and benefits	85.4	86.9	88.2	77.2	73	75.5	76.6	70.6	337.7	295.7	263.9
Clearing and related expenses	43.1	49	50.7	36.9	35.1	33.9	33.7	33.6	179.7	136.3	129.9
Introducing broker commissions	32.4	34.1	36.2	31.1	26.9	29.2	28.2	28.7	133.8	113	68.9
Occupancy and equipment rental									16.5	15.2	13.3
Professional fees									18.1	15.2	14
Travel and business development									13.8	13.3	11.5
Non-trading technology and support									13.9	11.6	7.1
Depreciation and amortization									11.6	9.8	8.2
Communications									5.4	5	4.7
Bad debts	1.2	1.6	0.2	0.1	0.4	0.1	1.3	2.5	3.1	4.3	4.4
Other	35.3	35.2	36.4	33.4	33.2	32.7	31.7	32.8	26.3	25.9	22.3
Total non-interest expenses	121.9	123.7	124.8	111.7	153.6	108.3	109.6	105.9	482.1	477.4	377.4
Loss from continuing operations, before tax	(20.5)	(32.9)	(29.5)	(18.6)	22.5	(15)	(14.3)	(8.4)	(101.5)	(15.2)	(72.7)
Income tax benefit	$ (4.8)	$ (8.9)	$ (6.8)	$ (25.5)	$ (1.1)	$ (2.3)	$ (3.3)	$ (2.1)	(46)	(8.8)	(18)
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Management fees from affiliates									40.4	39.1	30.1
Trading gains, net									0	(1)	0.7
Consulting fees									0	0	2.2
Interest income									2.3	1.2	1.8
Operating revenues									84.6	92	65.8
Interest expense									15.7	14.4	13.4
Net operating revenues									68.9	77.6	52.4
Non-interest expenses:
Compensation and benefits									73	60.3	52.8
Clearing and related expenses									1.1	1.2	1.7
Introducing broker commissions									0	0	0.6
Communication and data services									5.8	6.4	5.6
Occupancy and equipment rental									2.6	2.5	2.8
Professional fees									6.7	3.7	4.8
Travel and business development									2.6	2.7	1.7
Non-trading technology and support									9.1	7.4	4.7
Depreciation and amortization									4.8	3.3	2.5
Communications									0.9	0.9	1.1
Bad debts									0	0	0.2
Management services fee to affiliates									0	0	1.2
Other									6.9	5.6	7
Total non-interest expenses									113.5	94	86.7
Gain on acquisition									0	0	6.2
Loss from continuing operations, before tax									44.6	16.4	28.1
Income tax benefit									7.4	26.8	24.7
Net loss									(37.2)	10.4	(3.4)
Adjustment to Investment in Subs for Equity Method Accounting									$ 92.7	$ 4	$ 58.1

Condensed Parent Only Financi_5

Condensed Parent Only Financial Statements - Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2013
Condensed Financial Statements, Captions [Line Items]
Depreciation and amortization									$ 11.6	$ 9.8	$ 8.2
Bad debts	$ 1.2	$ 1.6	$ 0.2	$ 0.1	$ 0.4	$ 0.1	$ 1.3	$ 2.5	3.1	4.3	4.4
Deferred income taxes									22.3	(9.8)	(0.8)
Amortization and extinguishment of debt issuance costs									1	1.9	1.1
Amortization of share-based compensation expense									6.6	6.3	5.1
Deposits and receivables from broker-dealers, clearing organizations, and counterparties									408.8	(889.1)	146.6
Receivables from subsidiaries, net									(0.8)	(0.3)	(3.1)
Notes receivable, net									6.8	8.3	59.5
Income taxes receivable									(1.3)	0.5	8.2
Financial instruments owned, at fair value									(308.7)	(125.6)	(192.9)
Other assets									(3.3)	(16)	(17.4)
Accounts payable and other accrued liabilities									18.6	(19.6)	7.5
Payable to customers									520	290.9	172.2
Financial instruments sold, not yet purchased, at fair value									153.9	(124.4)	273.9
Net cash (used in) provided by operating activities									(74)	13.9	(27.8)
Purchase of property and equipment									(12.5)	(16.1)	(15.4)
Net cash used in investing activities									(15.4)	(22.3)	(35.5)
Payable to lenders under loans									125.8	48.2	142
Payments of notes payable									(0.8)	(0.8)	(0.8)
Payments related to earn-outs on acquisitions									(5.5)	0	(2.9)
Share repurchase									0	0	(19.5)
Debt issuance costs									(0.4)	(0.3)	(2.1)	$ (1.7)
Exercise of stock options									2.6	3.4	3.5
Payments Related to Tax Withholding for Share-based Compensation									(0.8)	0	0
Income tax benefit on stock options and awards									0	0.7	0.8
Net cash provided by (used in) financing activities									120.9	5.7	121
Net (decrease) increase in cash and cash equivalents									27.4	(1.3)	48.1
Cash and cash equivalents at beginning of period				314.9				316.2	314.9	316.2	268.1
Cash and cash equivalents at end of period	342.3				314.9				342.3	314.9	316.2
Cash paid for interest									78.9	38	26
Income taxes (received) paid, net of cash refunds									22.2	17.1	8.5
Additional consideration payable related to acquisitions									0	(0.2)	(0.4)
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Net loss									(37.2)	10.4	(3.4)
Depreciation and amortization									4.8	3.3	2.5
Bad debts									0	0	0.2
Deferred income taxes									18	(10.7)	(3.3)
Amortization and extinguishment of debt issuance costs									0.7	1.7	1
Amortization of share-based compensation expense									6.1	5.5	5.1
Business Combination, Bargain Purchase, Gain Recognized, Amount									0	0	6.2
Deposits and receivables from broker-dealers, clearing organizations, and counterparties									0	(2.9)	2.8
Due to/from subsidiaries									(68.6)	27	(86.6)
Notes receivable, net									2.9	2.1	39.1
Income taxes receivable									(6.6)	5.4	10.3
Financial instruments owned, at fair value									(4.4)	1.3	1.7
Other assets									(0.7)	7.8	0.3
Accounts payable and other accrued liabilities									8.6	(7.8)	0.4
Payable to customers									(0.3)	(2.5)	(26.1)
Financial instruments sold, not yet purchased, at fair value									34	(10.6)	35.9
Net cash (used in) provided by operating activities									(43.5)	35.5	(35)
Capital contribution in affiliates									(4.5)	0	(48.4)
Purchase of property and equipment									(5.9)	(6.1)	(5.5)
Net cash used in investing activities									(10.4)	(6.1)	(53.9)
Payable to lenders under loans									58.2	13.5	108.5
Proceeds from Issuance of Senior Long-term Debt									0	(45.5)	0
Payments related to earn-outs on acquisitions									(5.5)	0	(2.9)
Share repurchase									0	0	(19.5)
Debt issuance costs									0	0	(1.9)
Exercise of stock options									2.6	3.4	3.5
Payments Related to Tax Withholding for Share-based Compensation									(0.8)	0	0
Income tax benefit on stock options and awards									0	0.7	0.8
Net cash provided by (used in) financing activities									53.7	(28.7)	87.7
Net (decrease) increase in cash and cash equivalents									(0.2)	0.7	(1.2)
Cash and cash equivalents at beginning of period				$ 2				$ 1.3	2	1.3	2.5
Cash and cash equivalents at end of period	$ 1.8				$ 2				1.8	2	1.3
Cash paid for interest									15	8.2	9
Income taxes (received) paid, net of cash refunds									(18.4)	(22.3)	(33.8)
Additional consideration payable related to acquisitions									$ 0	$ (0.2)	$ (0.4)

Description of Business and S_6

Description of Business and Significant Accounting Policies - Accounting Standards Adopted (Details) $ in Millions	12 Months Ended
	Sep. 30, 2018USD ($)
Accounting Policies Adopted [Abstract]
Excess Tax Benefit from Share-based Compensation, Operating Activities	$ 0.5