Other Expenses - Other Expenses Breakout (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2010
Component of Operating Other Cost and Expense [Line Items]
Other Cost and Expense, Operating	$ 31.0	$ 28.5	$ 17.1
Travel and Entertainment Expense [Member]
Component of Operating Other Cost and Expense [Line Items]
Other Cost and Expense, Operating	11.2	8.9	6.3
Contingent Consideration [Member]
Component of Operating Other Cost and Expense [Line Items]
Other Cost and Expense, Operating	2.9	4.7	0
Insurance Expense [Member]
Component of Operating Other Cost and Expense [Line Items]
Other Cost and Expense, Operating	1.7	1.5	1.8
Advertising, Meetings and Conferences [Member]
Component of Operating Other Cost and Expense [Line Items]
Other Cost and Expense, Operating	2.4	1.8	1.7
Non-trading hardware and software maintenance and software licensing [Member]
Component of Operating Other Cost and Expense [Line Items]
Other Cost and Expense, Operating	2.2	2.8	1.3
Office supplies and printing [Member]
Component of Operating Other Cost and Expense [Line Items]
Other Cost and Expense, Operating	1.3	1.1	1.2
Taxes Other than Income and Excise Taxes [Member]
Component of Operating Other Cost and Expense [Line Items]
Other Cost and Expense, Operating	4.0	2.8	1.3
Other Operating Expense [Member]
Component of Operating Other Cost and Expense [Line Items]
Other Cost and Expense, Operating	$ 5.3	$ 4.9	$ 3.5