Consolidated Cash Flows Statements - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Cash flows from operating activities:
Net income	$ 6.4	$ 54.7	$ 55.7
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for bad debt on physical coal	47.0	0.0	0.0
Depreciation and amortization	9.8	7.8	7.2
Provision for bad debts	4.3	4.4	7.3
Deferred income taxes	(9.8)	(0.8)	4.8
Amortization and extinguishment of debt issuance costs	1.9	1.1	0.9
Actuarial gain on pension and postretirement benefits	(0.3)	0.0	0.0
Amortization of share-based compensation expense	6.3	5.1	3.6
(Gain) loss on sale of property and equipment	(0.3)	0.4	0.5
Gain on acquisition	0.0	(6.2)	0.0
Gain on sale of exchange memberships and common stock	0.0	0.0	(1.2)
Changes in operating assets and liabilities, net:
Cash, securities and other assets segregated under federal and other regulations	622.7	(379.9)	(315.0)
Change in securities purchased under agreements to resell	203.0	(285.1)	15.2
Securities borrowed	(79.7)	0.0	0.0
Deposits and receivables from broker-dealers, clearing organizations, and counterparties	(889.1)	146.6	44.9
Receivable from customers, net	(116.4)	97.8	(169.0)
Notes receivable, net	8.3	59.5	(14.5)
Income taxes receivable	0.5	8.2	0.0
Financial instruments owned, at fair value	(125.6)	(192.9)	(565.0)
Physical commodities inventory	(1.7)	(91.0)	7.1
Other assets	(16.0)	(17.4)	(16.2)
Accounts payable and other accrued liabilities	(19.6)	7.5	23.2
Payable to customers	290.9	172.2	332.1
Payable to broker-dealers, clearing organizations and counterparties	(124.1)	(53.8)	251.1
Income taxes payable	0.2	0.3	1.7
Securities sold under agreements to repurchase	226.0	159.8	186.0
Securities loaned	93.6	0.0	0.0
Financial instruments sold, not yet purchased, at fair value	(124.4)	273.9	177.5
Net cash provided by (used in) provided by operating activities	13.9	(27.8)	37.9
Cash flows from investing activities:
Cash paid for acquisitions, net	(6.0)	(20.0)	(7.8)
Purchase of exchange memberships and common stock	(0.2)	(0.1)	(0.7)
Sale of exchange memberships and common stock	0.0	0.0	2.1
Purchase of property and equipment	(16.1)	(15.4)	(9.1)
Net cash used in investing activities	(22.3)	(35.5)	(15.5)
Cash flows from financing activities:
Net change in payable to lenders under loans	48.2	142.0	15.5
Payments related to earn-outs on acquisitions	0.0	(2.9)	(2.2)
Repayment of senior unsecured notes	(45.5)	0.0	0.0
Proceeds from notes payable	0.0	0.0	4.0
Repayment of note payable	0.8	0.8	0.4
Share repurchase	0.0	(19.5)	(4.7)
Debt issuance costs	(0.3)	(2.1)	(0.2)
Exercise of stock options	3.4	3.5	2.5
Income tax benefit on stock options and awards	0.7	0.8	0.5
Net cash provided by financing activities	5.7	121.0	15.0
Effect of exchange rates on cash and cash equivalents	1.4	(9.6)	(0.6)
Net increase in cash and cash equivalents	(1.3)	48.1	36.8
Cash and cash equivalents at beginning of period	316.2	268.1	231.3
Cash and cash equivalents at end of period	314.9	316.2	268.1
Supplemental disclosure of cash flow information:
Cash paid for interest	38.0	26.0	15.8
Income taxes paid, net of cash refunds	17.1	8.5	15.3
Supplemental disclosure of non-cash investing and financing activities:
Identified intangible assets and goodwill on acquisitions	0.0	0.0	1.6
Additional consideration payable related to acquisitions	(0.2)	(0.4)	1.9
Acquisition of business:
Assets acquired	0.0	187.1	1,011.4
Liabilities acquired	0.0	(136.0)	(995.1)
Total net assets acquired	0.0	51.1	16.3
Deferred consideration payable related to acquisitions	0.0	0.0	5.0
Escrow releases and deposits related to acquisitions	$ (5.0)
Escrow deposits related to acquisitions		$ 3.4	$ 5.0