Consolidated Statements of Comprehensive Income Statement - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Statement of Comprehensive Income [Abstract]
Net income	$ 55.7	$ 19.3	$ 19.3
Other comprehensive income (loss), net of tax [Abstract]
Foreign currency translation adjustment	(4.0)	(4.6)	(1.8)
Pension liabilities adjustment	(1.5)	(0.8)	2.9
Net unrealized gain or loss on available-for-sale securities	2.7	0.2	0.6
Reclassification of adjustment for gains included in net income:
Foreign currency translation adjustment (included in other income)	0.0	0.0	(0.1)
Periodic pension costs (included in compensation and benefits)	0.3	0.2	0.8
Realized gain on available-for-sale securities (included in trading gains, net and interest income)	(5.4)	(0.1)	(8.3)
Income tax expense from reclassification adjustments (included in income tax expense)	2.0	(0.1)	1.7
Reclassification adjustment for gains included in net income	(3.1)	0.0	(5.9)
Other comprehensive loss	(5.9)	(5.2)	(4.2)
Comprehensive income	$ 49.8	$ 14.1	$ 15.1