Derivative Financial Instruments Derivative Financial Instruments (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Net losses on foreign currency exposures	$ 5.7	$ 1.9	$ 2.7
Net realized and unrealized gain or (loss) (excluding the underlying foreign currency exposure being hedged)	$ (1.8)	$ (0.5)	$ 0.6