Basis of Presentation and Consolidation and Recently Issued Accounting Standards (Details) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jun. 30, 2017
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Net Income	$ 0.2
Payments Related to Tax Withholding for Share-based Compensation	$ 0.8	$ 0.0
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		2.9
Communications
Prior Period Reclassification Adjustment		$ 1.2