Other Expenses Other Expenses - Other Expenses Breakout (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Component of Operating Other Cost and Expense [Line Items]
Other Cost and Expense, Operating	$ 9.2	$ 8.9
Travel and Entertainment Expense [Member]
Component of Operating Other Cost and Expense [Line Items]
Other Cost and Expense, Operating	3.0	3.2
Contingent Consideration [Member]
Component of Operating Other Cost and Expense [Line Items]
Other Cost and Expense, Operating	0.7	1.3
Insurance Expense [Member]
Component of Operating Other Cost and Expense [Line Items]
Other Cost and Expense, Operating	0.5	0.4
Advertising, Meetings and Conferences [Member]
Component of Operating Other Cost and Expense [Line Items]
Other Cost and Expense, Operating	0.4	0.6
Non-trading hardware and software maintenance and software licensing [Member]
Component of Operating Other Cost and Expense [Line Items]
Other Cost and Expense, Operating	0.6	0.6
Office supplies and printing [Member]
Component of Operating Other Cost and Expense [Line Items]
Other Cost and Expense, Operating	0.3	0.3
Taxes Other than Income and Excise Taxes [Member]
Component of Operating Other Cost and Expense [Line Items]
Other Cost and Expense, Operating	1.1	0.7
Other Operating Expense [Member]
Component of Operating Other Cost and Expense [Line Items]
Other Cost and Expense, Operating	$ 2.6	$ 1.8