Goodwill and Intangible Assets - Changes to the Carrying Amount of Goodwill by Segment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Goodwill [Roll Forward]
Beginning Balance	$ 2,930,205	$ 2,937,260
Additions due to an acquisition
Foreign currency translation impact	9,654	(7,055)
Impairment loss	(150,000)	0	$ 0
Reclassified as held-for-sale	(49,057)
Ending Balance	2,740,802	2,930,205	2,937,260
Accumulated impairment losses	(150,000)
Digital Markets Reporting Unit
Goodwill [Roll Forward]
Impairment loss	(150,000)
Insights
Goodwill [Roll Forward]
Beginning Balance	2,453,880	2,460,448
Additions due to an acquisition
Foreign currency translation impact	6,435	(6,568)
Impairment loss	0
Reclassified as held-for-sale	0
Ending Balance	2,460,315	2,453,880	2,460,448
Accumulated impairment losses	0
Conferences
Goodwill [Roll Forward]
Beginning Balance	183,920	183,997
Additions due to an acquisition
Foreign currency translation impact	132	(77)
Impairment loss	0
Reclassified as held-for-sale	0
Ending Balance	184,052	183,920	183,997
Accumulated impairment losses	0
Consulting
Goodwill [Roll Forward]
Beginning Balance	95,304	95,714
Additions due to an acquisition
Foreign currency translation impact	1,131	(410)
Impairment loss	0
Reclassified as held-for-sale	0
Ending Balance	96,435	95,304	95,714
Accumulated impairment losses	0
Other
Goodwill [Roll Forward]
Beginning Balance	197,101	197,101
Additions due to an acquisition
Foreign currency translation impact	1,956	0
Impairment loss	(150,000)
Reclassified as held-for-sale	(49,057)
Ending Balance	0	$ 197,101	$ 197,101
Accumulated impairment losses	$ (150,000)