Condensed Parent Only Financial Statements [Schedule] Cash Flows (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2010
Condensed Financial Statements, Captions [Line Items]
Net Income (Loss) Attributable to Parent	$ 15.0	$ 37.3	$ 5.4
Depreciation, Depletion and Amortization, Nonproduction	7.2	4.7	1.7
Tangible Asset Impairment Charges	1.7	6.2	3.5
Deferred Income Tax Expense (Benefit)	(0.5)	1.8	1.2
Amortization of Financing Costs and Discounts	1.7	1.6	0.2
Convertible debt interest settled in company stock upon conversion	0	0.2	0
Share-based Compensation	5.9	2.3	1.9
Gain on acquisition of INTL Provident	0	(0.4)	0
Notes receivable, net	(77.9)	2.9	(7.0)
Income taxes receivable	(3.1)	0.6	35.4
Financial instruments owned, at fair value	58.3	280.7	(212.7)
Other assets	(1.6)	(12.1)	3.9
Increase (Decrease) in Accounts Payable and Accrued Liabilities	10.6	30.8	1.9
Increase (Decrease) in Payables to Customers	248.0	366.2	415.3
Increase (Decrease) in Financial Instruments Sold, Not yet Purchased	(215.5)	202.9	(46.7)
Net Cash Provided by (Used in) Operating Activities	(92.1)	209.0	113.0
Cash paid for other acquisitions, net	(11.7)	(9.3)	(37.6)
Payments to Acquire Property, Plant, and Equipment	(8.7)	(10.1)	(4.7)
Net Cash Provided by (Used in) Investing Activities	(20.0)	(21.5)	(42.4)
Net change in payable to lenders under loans	140.8	(37.5)	6.1
Share repurchase	(4.0)	0	0
Debt issuance costs	(0.3)	(2.4)	0
Exercise of stock options	1.9	1.4	0.7
Excess Tax Benefit (Tax Deficiency) from Share-based Compensation, Financing Activities	0.2	0	0
Net Cash Provided by (Used in) Financing Activities	129.0	(48.4)	(49.2)
Cash and Cash Equivalents, Period Increase (Decrease)	15.7	138.7	21.4
Cash and Cash Equivalents, at Carrying Value	236.3	220.6	81.9
Cash paid for interest	7.9	9.5	7.4
Income taxes paid, net of cash refunds	6.1	17.6	(33.3)
Convertible note conversions		16.9
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Net Income (Loss) Attributable to Parent	(14.5)	(10.0)	3.3
Depreciation, Depletion and Amortization, Nonproduction	1.2	0.6	0
Tangible Asset Impairment Charges	2.2	0	0
Deferred Income Tax Expense (Benefit)	(0.1)	1.1	(1.6)
Amortization of Financing Costs and Discounts	0.5	0.2	0.2
Convertible debt interest settled in company stock upon conversion	0	0.2	0
Share-based Compensation	5.9	2.3	1.9
Gain on acquisition of INTL Provident	0	(0.4)	0
Increase (Decrease) Due from Affiliates	21.7	35.7	(6.5)
Notes receivable, net	(10.2)	0	0
Income taxes receivable	7.1	(13.6)	(0.5)
Financial instruments owned, at fair value	1.7	(0.4)	(2.8)
Other assets	(0.3)	(0.8)	(0.3)
Increase (Decrease) in Accounts Payable and Accrued Liabilities	(2.2)	1.7	(1.3)
Increase (Decrease) in Payables to Customers	0.7	0	0
Increase (Decrease) in Financial Instruments Sold, Not yet Purchased	(33.4)	(0.5)	37.1
Net Cash Provided by (Used in) Operating Activities	(19.7)	16.1	28.4
Cash paid for other acquisitions, net	0	0	(5.0)
Payments for Advance to Affiliate	(12.5)	(1.0)	(0.7)
Payments to Acquire Property, Plant, and Equipment	(2.7)	(1.7)	0
Net Cash Provided by (Used in) Investing Activities	(15.2)	(2.7)	(5.7)
Net change in payable to lenders under loans	48.0	(11.9)	(23.0)
Share repurchase	(4.0)	0	0
Debt issuance costs	(0.1)	(1.2)	0
Exercise of stock options	1.9	1.3	0.7
Excess Tax Benefit (Tax Deficiency) from Share-based Compensation, Financing Activities	0.2	0	0
Net Cash Provided by (Used in) Financing Activities	46.0	(11.8)	(22.3)
Cash and Cash Equivalents, Period Increase (Decrease)	11.1	1.6	0.4
Cash and Cash Equivalents, at Carrying Value	13.1	2.0	0.4
Cash paid for interest	2.1	3.0	3.8
Income taxes paid, net of cash refunds	0.1	10.8	(1.7)
Convertible note conversions	$ 0	$ 16.7	$ 0