Assets and Liabilities, at Fair Value - Contingent Consideration (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014	Sep. 30, 2014
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Payments to Acquire Businesses, Gross			$ 3.4
Equity Investments in Exchange Stock - Fair Value	5.7		5.7		4.8
Equity Investments in Exchange Stock - Cost	3.7		3.7		3.7
Change in fair value of contingent consideration for acquisitions	0.1	0.1	1.7	0.3
Contingent Consideration [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Change in fair value of contingent consideration for acquisitions			$ 0.2	$ 0.3