Condensed Consolidated Cash Flows Statements - USD ($) $ in Millions	6 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Cash flows from operating activities:
Net income	$ 17.3	$ 23.3
Adjustments to reconcile net income to net cash (used in) provided by operating activities:
Depreciation and amortization	4.8	3.9
Bad debts	3.8	4.6
Deferred income taxes	(3.6)	(1.8)
Amortization of debt issuance costs and debt discount	1.4	0.5
Amortization of stock-based compensation	2.6	2.5
Loss on sale of property and equipment	0.3	(0.3)
Changes in operating assets and liabilities, net:
Cash, securities and other assets segregated under federal and other regulations	47.4	(174.1)
Securities purchased under agreements to resell	(129.2)	(377.0)
Increase (Decrease) in Securities Borrowed	(66.7)	0.0
Deposits and receivables from exchange-clearing organizations	(158.4)	111.7
Deposits and receivables from broker-dealers, clearing organizations, and counterparties	32.1	128.5
Receivables from customers, net	(2.5)	108.8
Notes receivable, net	7.9	12.7
Income taxes receivable	0.0	0.5
Financial instruments owned, at fair value	(304.8)	(454.5)
Physical commodities inventory	(58.2)	1.6
Other assets	7.8	(4.8)
Accounts payable and other accrued liabilities	(8.8)	(25.6)
Payables to customers	27.8	(144.6)
Payables to broker-dealers, clearing organizations and counterparties	(64.3)	62.3
Income taxes payable	0.9	(0.1)
Payables under repurchase agreements	264.8	108.3
Increase (Decrease) in Securities Loaned Transactions	89.9	0.0
Financial instruments sold, not yet purchased, at fair value	243.7	465.7
Net cash (used in) provided by operating activities	(44.6)	(147.3)
Cash flows from investing activities:
Cash paid for acquisitions, net	6.0	0.0
Purchase of property and equipment	6.1	8.0
Net cash used in investing activities	(12.1)	(8.0)
Cash flows from financing activities:
Net change in payable to lenders under loans	81.0	110.3
Repayments of Unsecured Debt	(45.5)	0.0
Payments of note payable	0.4	0.4
Deferred payments on acquisitions	0.0	2.7
Debt issuance costs	0.1	1.9
Exercise of stock options	2.5	1.7
Share repurchases	0.0	10.3
Excess income tax benefit on stock options and awards	(0.2)	0.7
Net cash provided by financing activities	37.3	97.4
Effect of exchange rates on cash and cash equivalents	(0.5)	(7.0)
Net (decrease) increase in cash and cash equivalents	(19.9)	(64.9)
Cash and cash equivalents at beginning of period	316.2	268.1
Cash and cash equivalents at end of period	296.3	203.2
Supplemental disclosure of cash flow information:
Cash paid for interest	17.1	11.8
Income taxes paid, net of cash refunds	8.1	9.2
Supplemental disclosure of non-cash investing and financing activities:
Identified intangible assets and goodwill on acquisitions	6.0	0.0
Additional consideration payable related to acquisitions, net	$ 0.0	$ 0.3