Other Expenses - Other Expenses Breakout (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Component of Operating Other Cost and Expense [Line Items]
Other Cost and Expense, Operating	$ 8.4	$ 7.4	$ 25.4	$ 24.8
Travel and Entertainment Expense [Member]
Component of Operating Other Cost and Expense [Line Items]
Other Cost and Expense, Operating	2.7	2.3	7.9	8.6
Contingent Consideration [Member]
Component of Operating Other Cost and Expense [Line Items]
Other Cost and Expense, Operating	0.7	0.5	1.9	2.7
Insurance Expense [Member]
Component of Operating Other Cost and Expense [Line Items]
Other Cost and Expense, Operating	0.5	0.4	1.4	1.2
Advertising, Meetings and Conferences [Member]
Component of Operating Other Cost and Expense [Line Items]
Other Cost and Expense, Operating	0.6	0.7	1.7	1.8
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	0.4	2.2	1.8
Office supplies and printing [Member]
Component of Operating Other Cost and Expense [Line Items]
Other Cost and Expense, Operating	0.3	0.3	1.0	1.0
Taxes Other than Income and Excise Taxes [Member]
Component of Operating Other Cost and Expense [Line Items]
Other Cost and Expense, Operating	1.9	1.1	4.1	3.0
Other Operating Expense [Member]
Component of Operating Other Cost and Expense [Line Items]
Other Cost and Expense, Operating	$ 1.1	$ 1.7	$ 5.2	$ 4.7