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Revenue and Related Matters - Disaggregation of Revenue by Geographic Area (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020
Disaggregation of Revenue [Line Items] |  |  |
Total revenues | $ 5,475,846 | $ 4,733,962 | $ 4,099,403
United States and Canada |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Total revenues | 3,619,382 | 3,048,902 | 2,637,824
Europe, Middle East and Africa |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Total revenues | 1,234,659 | 1,130,979 | 966,273
Other International |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Total revenues | 621,805 | 554,081 | 495,306
Research |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Total revenues | 4,604,791 | 4,101,392 | 3,602,892
Research | United States and Canada |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Total revenues | 3,056,096 | 2,655,534 | 2,339,482
Research | Europe, Middle East and Africa |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Total revenues | 1,017,860 | 958,339 | 826,752
Research | Other International |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Total revenues | 530,835 | 487,519 | 436,658
Conferences |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Total revenues | 389,273 | 214,449 | 120,140
Conferences | United States and Canada |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Total revenues | 263,165 | 146,707 | 75,024
Conferences | Europe, Middle East and Africa |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Total revenues | 88,979 | 47,883 | 28,108
Conferences | Other International |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Total revenues | 37,129 | 19,859 | 17,008
Consulting |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Total revenues | 481,782 | 418,121 | 376,371
Consulting | United States and Canada |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Total revenues | 300,121 | 246,661 | 223,318
Consulting | Europe, Middle East and Africa |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Total revenues | 127,820 | 124,757 | 111,413
Consulting | Other International |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Total revenues | $ 53,841 | $ 46,703 | $ 41,640

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- Definition Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 30 -Subparagraph (a) -URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8906-108599 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 40 -URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e9031-108599 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 41 -Subparagraph (a) -URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e9038-108599 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 32 -Subparagraph (b) -URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8933-108599 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 32 -Subparagraph (a) -URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8933-108599 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 50 -Paragraph 4 -Subparagraph (a) -URI https://asc.fasb.org/extlink&oid=126920106&loc=SL49130543-203045 Reference 7: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 22 -Subparagraph (b) -URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8736-108599 Reference 8: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 22 -Subparagraph (a) -URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8736-108599 Reference 9: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 42 -URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e9054-108599 Reference 10: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 50 -Paragraph 5 -URI https://asc.fasb.org/extlink&oid=126920106&loc=SL49130545-203045 Reference 11: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 924 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 11.L) -URI https://asc.fasb.org/extlink&oid=6472922&loc=d3e499488-122856 + Details
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