Condensed Consolidated Cash Flows Statements - USD ($) $ in Millions	9 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Cash flows from operating activities:
Net income	$ 34.6	$ 13.5
Adjustments to reconcile net income to net cash (used in) provided by operating activities:
Depreciation and amortization	5.4	5.4
Provision for bad debts and impairments	3.2	0.8
Deferred income taxes	3.9	(3.6)
Amortization of debt issuance costs and debt discount	0.7	0.8
Amortization of stock-based compensation	2.8	3.2
Loss on sale of property and equipment	0.4	0.3
Changes in operating assets and liabilities, net:
Cash, securities and other assets segregated under federal and other regulations	(421.2)	29.5
Securities purchased under agreements to resell	(0.8)	0.0
Deposits and receivables from exchange-clearing organizations	579.2	(287.7)
Deposits and receivables from broker-dealers, clearing organizations, and counterparties	(17.4)	11.0
Receivable from customers, net	(77.3)	(38.6)
Notes receivable from customers, net	(3.5)	(20.6)
Income taxes receivable	(1.0)	1.8
Financial instruments owned, at fair value	(449.8)	(104.0)
Physical commodities inventory	(6.1)	7.0
Other assets	(16.1)	(5.5)
Accounts payable and other accrued liabilities	(6.5)	(6.5)
Payable to customers	(66.6)	249.8
Payable to broker-dealers, clearing organizations and counterparties	49.9	(14.0)
Income taxes payable	(1.7)	4.4
Payables under repurchase agreements	260.3	0.0
Financial instruments sold, not yet purchased, at fair value	132.3	92.5
Net cash (used in) provided by operating activities	4.7	(60.5)
Cash flows from investing activities:
Cash paid for acquisitions, net	7.8	0.0
Purchase of exchange memberships and common stock	0.7	0.0
Purchase of property and equipment	(7.4)	(4.1)
Net cash (used in) provided by investing activities	(15.9)	(4.1)
Cash flows from financing activities:
Net change in payable to lenders under loans	48.6	18.0
Proceeds from note payable	4.0	0.0
Payments of note payable	(0.2)	0.0
Payments related to earn-outs on acquisitions	(2.2)	(1.5)
Debt issuance costs	(0.1)	(0.3)
Exercise of stock options	2.5	1.4
Share repurchases	(4.7)	(9.7)
Income tax expense on stock options and awards	0.5	0.0
Net cash provided by (used in) financing activities	48.4	7.9
Effect of exchange rates on cash and cash equivalents	(0.5)	(1.7)
Net decrease in cash and cash equivalents	36.7	(58.4)
Cash and cash equivalents at beginning of period	231.3	156.1
Cash and cash equivalents at end of period	268.0	97.7
Supplemental disclosure of cash flow information:
Cash paid for interest	7.8	7.4
Income taxes paid, net of cash refunds	12.4	1.0
Supplemental disclosure of non-cash investing and financing activities:
Identified intangible assets and goodwill on acquisitions	3.0	0.5
Additional consideration payable related to acquisitions, net	1.9	0.6
Acquisition of business:
Assets acquired	1,011.4	0.0
Liabilities assumed	(995.1)	0.0
Total net assets acquired	16.3	0.0
Deferred consideration payable related to acquisitions	5.0	0.0
Escrow deposits related to acquisitions	$ 5.0	$ 0.0