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Revenue and Related Matters - Disaggregation of Revenue by Geographic Area (Details) - USD ($) $ in Thousands | 3 Months Ended
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Mar. 31, 2022 | Mar. 31, 2021
Disaggregation of Revenue [Line Items] |  |
Total revenues | $ 1,262,740 | $ 1,104,038
Research |  |
Disaggregation of Revenue [Line Items] |  |
Total revenues | 1,136,380 | 979,732
Conferences |  |
Disaggregation of Revenue [Line Items] |  |
Total revenues | 10,354 | 24,802
Consulting |  |
Disaggregation of Revenue [Line Items] |  |
Total revenues | 116,006 | 99,504
United States and Canada |  |
Disaggregation of Revenue [Line Items] |  |
Total revenues | 816,970 | 708,418
United States and Canada | Research |  |
Disaggregation of Revenue [Line Items] |  |
Total revenues | 740,529 | 631,333
United States and Canada | Conferences |  |
Disaggregation of Revenue [Line Items] |  |
Total revenues | 7,652 | 19,599
United States and Canada | Consulting |  |
Disaggregation of Revenue [Line Items] |  |
Total revenues | 68,789 | 57,486
Europe, Middle East and Africa |  |
Disaggregation of Revenue [Line Items] |  |
Total revenues | 296,811 | 263,276
Europe, Middle East and Africa | Research |  |
Disaggregation of Revenue [Line Items] |  |
Total revenues | 263,129 | 230,201
Europe, Middle East and Africa | Conferences |  |
Disaggregation of Revenue [Line Items] |  |
Total revenues | 1,238 | 2,713
Europe, Middle East and Africa | Consulting |  |
Disaggregation of Revenue [Line Items] |  |
Total revenues | 32,444 | 30,362
Other International |  |
Disaggregation of Revenue [Line Items] |  |
Total revenues | 148,959 | 132,344
Other International | Research |  |
Disaggregation of Revenue [Line Items] |  |
Total revenues | 132,722 | 118,198
Other International | Conferences |  |
Disaggregation of Revenue [Line Items] |  |
Total revenues | 1,464 | 2,490
Other International | Consulting |  |
Disaggregation of Revenue [Line Items] |  |
Total revenues | $ 14,773 | $ 11,656

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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 http://asc.fasb.org/extlink&oid=123359005&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 http://asc.fasb.org/extlink&oid=123359005&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 http://asc.fasb.org/extlink&oid=123359005&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 http://asc.fasb.org/extlink&oid=123359005&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 http://asc.fasb.org/extlink&oid=123359005&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 http://asc.fasb.org/extlink&oid=123351226&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 http://asc.fasb.org/extlink&oid=123359005&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 http://asc.fasb.org/extlink&oid=123359005&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 http://asc.fasb.org/extlink&oid=123359005&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 http://asc.fasb.org/extlink&oid=123351226&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 http://asc.fasb.org/extlink&oid=6472922&loc=d3e499488-122856 + Details
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