Consolidated Balance Sheets (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Sep. 30, 2012	Sep. 30, 2011
Assets [Abstract]
Securities and other assets segregated, fair value	$ 72.8	$ 22.7
Dep and rec -exch clear org - fair value	1,510.0	1,408.2
Receivables from Brokers-Dealers and Clearing Organizations	(0.7)	16.2
Accounts Payable and Other Accrued Liabilities	$ 14.8	$ 22.3
Preferred stock - par value	$ 0.01	$ 0.01
Preferred stock - authorized	1,000,000	1,000,000
Preferred stock - issued	0	0
Preferred stock - outstanding	0	0
Common stock - par value	$ 0.01	$ 0.01
Common stock - authorized	30,000,000	30,000,000
Common stock - issued	19,214,219	18,653,964
Common stock - outstanding	18,984,951	18,642,407
Treasury Stock - Shares	229,064	11,557