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Basis of Presentation and Consolidation and Recently Issued Accounting Standards (Details) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Mar. 31, 2017 USD ($) | Mar. 31, 2018 USD ($) | Mar. 31, 2017 USD ($)
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Net Income |  | $ 0.3 |
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 | $ 2.8 |  | 5.7
Communications |  |  |
Prior Period Reclassification Adjustment | $ 1.2 |  | $ 2.4

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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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- Definition Amount of cash outflow to satisfy an employee's income tax withholding obligation as part of a net-share settlement of a share-based award. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 25 -Paragraph 19A -URI http://asc.fasb.org/extlink&oid=96949009&loc=SL79513924-113897 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 15 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3291-108585 + Details
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