Condensed Consolidated Cash Flows Statements - USD ($) $ in Millions	9 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Cash flows from operating activities:
Net income	$ 37.9	$ 34.6
Adjustments to reconcile net income to net cash (used in) provided by operating activities:
Depreciation and amortization	5.8	5.4
Bad debts	4.6	3.2
Deferred income taxes	0.9	3.9
Amortization of debt issuance costs and debt discount	0.7	0.7
Amortization of stock-based compensation	3.8	2.8
Loss on sale of property and equipment	(0.4)	(0.4)
Changes in operating assets and liabilities, net:
Cash, securities and other assets segregated under federal and other regulations	(218.0)	(421.2)
Securities purchased under agreements to resell	(301.3)	(0.8)
Deposits and receivables from exchange-clearing organizations	51.5	579.2
Deposits and receivables from broker-dealers, clearing organizations, and counterparties	96.1	(17.4)
Receivables from customers, net	101.8	(77.3)
Notes receivable, net	28.5	(3.5)
Income taxes receivable	1.4	(1.0)
Financial instruments owned, at fair value	(562.4)	(449.8)
Physical commodities inventory	(73.8)	(6.1)
Other assets	(7.1)	(16.1)
Accounts payable and other accrued liabilities	(2.3)	(6.5)
Payables to customers	75.6	(66.6)
Payables to broker-dealers, clearing organizations and counterparties	(8.9)	49.9
Income taxes payable	0.0	(1.7)
Payables under repurchase agreements	429.0	260.3
Financial instruments sold, not yet purchased, at fair value	304.0	132.3
Net cash (used in) provided by operating activities	(31.8)	4.7
Cash flows from investing activities:
Cash paid for acquisitions, net	0.0	7.8
Purchase of exchange memberships and common stock	0.0	0.7
Purchase of property and equipment	(12.1)	(7.4)
Net cash used in investing activities	(12.1)	(15.9)
Cash flows from financing activities:
Net change in payable to lenders under loans	170.6	48.6
Payments of note payable	(0.6)	(0.2)
Deferred payments on acquisitions	(2.7)	(2.2)
Debt issuance costs	(1.9)	(0.1)
Exercise of stock options	2.3	2.5
Share repurchases	(19.5)	(4.7)
Excess income tax benefit on stock options and awards	0.7	0.5
Net cash provided by financing activities	148.9	48.4
Effect of exchange rates on cash and cash equivalents	(8.5)	(0.5)
Net (decrease) increase in cash and cash equivalents	96.5	36.7
Cash and cash equivalents at beginning of period	268.1	231.3
Cash and cash equivalents at end of period	364.6	268.0
Supplemental disclosure of cash flow information:
Cash paid for interest	18.9	7.8
Income taxes paid, net of cash refunds	12.4	12.4
Supplemental disclosure of non-cash investing and financing activities:
Identified intangible assets and goodwill on acquisitions	0.0	3.0
Additional consideration payable related to acquisitions, net	0.3	1.9
Acquisition of business:
Assets acquired	0.0	1,011.4
Liabilities assumed	0.0	(995.1)
Total net assets acquired	0.0	16.3
Deferred consideration payable related to acquisitions	0.0	5.0
Escrow deposits related to acquisitions	$ 0.0	$ 5.0