Condensed Consolidated Cash Flows Statements - USD ($) $ in Millions	6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash flows from operating activities:
Net income	$ 15.8	$ 17.3
Adjustments to reconcile net income to net cash used in operating activities:
Depreciation and amortization	5.6	4.8
Bad debts	1.3	3.8
Deferred income taxes	18.6	(3.6)
Amortization of debt issuance costs	0.5	1.4
Amortization of stock-based compensation	3.2	2.6
Gain on sale of property and equipment	0.0	(0.3)
Changes in operating assets and liabilities, net:
Cash, securities and other assets segregated under federal and other regulations	(758.1)	47.4
Securities purchased under agreements to resell	(198.1)	(129.2)
Securities borrowed	(433.3)	(66.7)
Deposits with and receivables from broker-dealers, clearing organizations, and counterparties	755.0	(126.3)
Receivables from customers, net	(72.0)	(2.5)
Notes receivable, net	(1.9)	7.9
Income taxes receivable	(0.6)	0.0
Financial instruments owned, at fair value	(125.2)	(304.8)
Physical commodities inventory, net	(162.5)	(58.2)
Other assets	3.1	7.8
Accounts payable and other accrued liabilities	1.5	(8.8)
Payables to customers	195.6	27.8
Payables to broker-dealers, clearing organizations and counterparties	(51.0)	(64.3)
Income taxes payable	4.5	0.9
Securities sold under agreements to repurchase	169.5	264.8
Securities loaned	448.0	89.9
Financial instruments sold, not yet purchased, at fair value	104.1	243.7
Net cash used in operating activities	(76.4)	(44.6)
Cash flows from investing activities:
Cash paid for acquisitions, net	0.0	(6.0)
Purchase of property and equipment	(6.9)	(6.1)
Net cash used in investing activities	(6.9)	(12.1)
Cash flows from financing activities:
Net change in payable to lenders under loans	110.7	81.0
Repayment of senior unsecured notes	0.0	(45.5)
Payments of note payable	(0.4)	(0.4)
Deferred payments on acquisitions	(5.5)	0.0
Debt issuance costs	(0.1)	(0.1)
Exercise of stock options	2.2	2.5
Withholding taxes on stock option exercises	(0.8)	0.0
Income tax benefit on stock options and awards	0.0	(0.2)
Net cash provided by financing activities	106.1	37.3
Effect of exchange rates on cash and cash equivalents	(1.7)	(0.5)
Net (decrease) increase in cash and cash equivalents	21.1	(19.9)
Cash and cash equivalents at beginning of period	314.9	316.2
Cash and cash equivalents at end of period	336.0	296.3
Supplemental disclosure of cash flow information:
Cash paid for interest	32.5	17.1
Income taxes paid, net of cash refunds	9.8	8.1
Supplemental disclosure of non-cash investing and financing activities:
Identified intangible assets and goodwill on acquisitions	$ 0.0	$ 6.0