Other Expenses - Other Expenses Breakout (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Component of Operating Other Cost and Expense [Line Items]
Other Cost and Expense, Operating	$ 4.7	$ 6.6
Contingent Consideration [Member]
Component of Operating Other Cost and Expense [Line Items]
Other Cost and Expense, Operating	0.2	0.7
Insurance Expense [Member]
Component of Operating Other Cost and Expense [Line Items]
Other Cost and Expense, Operating	0.5	0.5
Advertising, meetings and conferences [Member]
Component of Operating Other Cost and Expense [Line Items]
Other Cost and Expense, Operating	0.4	0.4
Non-trading hardware and software maintenance and software licensing [Member]
Component of Operating Other Cost and Expense [Line Items]
Other Cost and Expense, Operating	0.7	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
Other clearing related expenses [Member]
Component of Operating Other Cost and Expense [Line Items]
Other Cost and Expense, Operating	0.4	0.4
Other non-income taxes [Member]
Component of Operating Other Cost and Expense [Line Items]
Other Cost and Expense, Operating	1.0	1.1
Other [Member]
Component of Operating Other Cost and Expense [Line Items]
Other Cost and Expense, Operating	$ 1.2	$ 2.6