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	1.0	47.0	0.0
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	1.0	1.9	1.1
Actuarial gain on pension and postretirement benefits	(0.3)	(0.3)	0.0
Amortization of share-based compensation expense	6.6	6.3	5.1
(Gain) loss on sale of property and equipment	0.0	(0.3)	0.4
Gain on acquisition	0.0	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)	203.0	(285.1)
Securities borrowed	(138.8)	(79.7)	0.0
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)	(91.0)
Other assets	(3.3)	(16.0)	(17.4)
Accounts payable and other accrued liabilities	18.6	(19.6)	7.5
Payable to customers	520.0	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	226.0	159.8
Securities loaned	166.8	93.6	0.0
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	(74.0)	13.9	(27.8)
Cash flows from investing activities:
Cash paid for acquisitions, net	(3.7)	(6.0)	(20.0)
Purchase of exchange memberships and common stock	0.0	(0.2)	(0.1)
Sale of exchange memberships and common stock	0.8	0.0	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	142.0
Payments related to earn-outs on acquisitions	(5.5)	0.0	(2.9)
Repayment of senior unsecured notes	0.0	(45.5)	0.0
Payments of notes payable	(0.8)	(0.8)	(0.8)
Share repurchase	0.0	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	0.0
Income tax benefit on stock options and awards	0.0	0.7	0.8
Net cash provided by financing activities	120.9	5.7	121.0
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	38.0	26.0
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	0.0
Additional consideration payable related to acquisitions	0.0	(0.2)	(0.4)
Acquisition of business:
Assets acquired	1.7	0.0	187.1
Liabilities acquired	(1.9)	0.0	(136.0)
Total net assets acquired	(0.2)	0.0	51.1
Escrow releases and deposits related to acquisitions	$ 0.0
Escrow deposits related to acquisitions		$ (5.0)	$ (3.4)