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Revenue and Related Matters - Timing Of Revenue Recognition Liabilities per Segment (Details) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2021 | Jun. 30, 2020 | Jun. 30, 2021 | Jun. 30, 2020
Disaggregation of Revenue [Line Items] |  |  |  |
Total revenues | $ 1,167,319 | $ 973,135 | $ 2,271,357 | $ 1,992,026
Transferred over time |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Total revenues | 1,002,743 | 879,194 | 1,981,172 | 1,789,814
Transferred at a point in time |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Total revenues | 164,576 | 93,941 | 290,185 | 202,212
Research |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Total revenues | 1,003,238 | 875,329 | 1,982,970 | 1,784,620
Research | Transferred over time |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Total revenues | 916,754 | 810,564 | 1,810,841 | 1,639,776
Research | Transferred at a point in time |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Total revenues | 86,484 | 64,765 | 172,129 | 144,844
Conferences |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Total revenues | 58,179 | 317 | 82,981 | 14,187
Conferences | Transferred over time |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Total revenues | 0 | 0 | 0 | 0
Conferences | Transferred at a point in time |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Total revenues | 58,179 | 317 | 82,981 | 14,187
Consulting |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Total revenues | 105,902 | 97,489 | 205,406 | 193,219
Consulting | Transferred over time |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Total revenues | 85,989 | 68,630 | 170,331 | 150,038
Consulting | Transferred at a point in time |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Total revenues | $ 19,913 | $ 28,859 | $ 35,075 | $ 43,181

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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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