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Goodwill and Intangible Assets - Changes to Carrying Amount of Goodwill by Reporting Unit (Details) - USD ($) | 3 Months Ended
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Mar. 31, 2022 | Sep. 30, 2021
Goodwill [Line Items] |  |
Goodwill impairment |  | $ 0
Goodwill [Roll Forward] |  |
Beginning balance | $ 2,951,317,000 |
Foreign currency translation impact | (1,996,000) |
Ending balance | 2,949,321,000 |
Goodwill, accumulated impairment losses | 0 |
Research |  |
Goodwill [Roll Forward] |  |
Beginning balance | 2,670,934,000 |
Foreign currency translation impact | (1,652,000) |
Ending balance | 2,669,282,000 |
Conferences |  |
Goodwill [Roll Forward] |  |
Beginning balance | 184,021,000 |
Foreign currency translation impact | (27,000) |
Ending balance | 183,994,000 |
Consulting |  |
Goodwill [Roll Forward] |  |
Beginning balance | 96,362,000 |
Foreign currency translation impact | (317,000) |
Ending balance | $ 96,045,000 |

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- Definition Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(10)(1)) -URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=120320667&loc=SL49117168-202975 Reference 3: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 852 -SubTopic 10 -Section 55 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=84165509&loc=d3e56426-112766 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=99380562&loc=d3e13770-109266 + Details
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