Condensed Consolidated Balance Sheets Parentheticals (USD $) In Millions, except Share data, unless otherwise specified	Jun. 30, 2014	Sep. 30, 2013
Balance Sheet Parentheticals [Abstract]
Securities and other assets segregated, fair value	$ 29.9	$ 107.6
Dep and rec -exch clear org - fair value	1,242.3	1,371.7
Dep and rec -b/d - fair value	(8.1)	(13.1)
Accounts pay and other accrued - fair value	$ 8.0	$ 9.6
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	19,819,720	19,638,330
Common stock - outstanding	18,876,747	19,209,157
Treasury stock - shares	942,973	429,173