Basis of Presentation and Consolidation and Recently Issued Accounting Standards (Details) $ in Millions	3 Months Ended	9 Months Ended
	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Net Income		$ 0.4
Payments Related to Tax Withholding for Share-based Compensation		$ 0.8
Number of different types of foreign currencies		140
Number of accounts for customers company-wide		20,000
Non-Trading Technology and Support [Member]
Prior Period Reclassification Adjustment	$ 3.2		8.9
Communications
Prior Period Reclassification Adjustment	$ 1.5		$ 3.9