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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 |

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- Definition Amount of the effect of a change in accounting principle on net income. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 250 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=64853466&loc=d3e22583-107794 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 250 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b)(2) -URI http://asc.fasb.org/extlink&oid=64853466&loc=d3e22499-107794 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 250 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=64853466&loc=d3e22580-107794 + Details
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