Segment Information - Schedule of Reconciliation of Segment Gross Contribution to Net Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Revenues	$ 1,511,041	$ 1,534,130
Personnel expenses	367,815	386,199
Product and content delivery expenses	42,800	68,612
Other expenses	14,119	14,022
Gross contribution	1,086,307	1,065,297
Cost of services and product development - unallocated	4,573	6,197
Selling, general and administrative	726,349	730,308
Depreciation and amortization	45,431	50,760
Gain from sale of divested operation	(6,138)	0
Interest expenses and other, net	23,680	11,024
Income before income taxes	292,412	267,008
Insights
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Revenues	1,294,195	1,255,569
Conferences
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Revenues	78,325	72,597
Consulting
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Revenues	119,129	139,706
Other
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Revenues	$ 19,392	$ 66,258
Maximum
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Percent of target bonus charges allocated to segments	100.00%	100.00%
Operating Segments | Insights
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Revenues	$ 1,294,195	$ 1,255,569
Personnel expenses	271,957	278,990
Product and content delivery expenses	3,630	4,396
Other expenses	7,091	6,236
Gross contribution	1,011,517	965,947
Operating Segments | Conferences
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Revenues	78,325	72,597
Personnel expenses	18,031	17,746
Product and content delivery expenses	26,756	24,172
Other expenses	3,130	3,297
Gross contribution	30,408	27,382
Operating Segments | Consulting
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Revenues	119,129	139,706
Personnel expenses	75,617	79,092
Product and content delivery expenses	2,939	3,263
Other expenses	3,768	3,959
Gross contribution	36,805	53,392
Operating Segments | Other
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Revenues	19,392	66,258
Personnel expenses	2,210	10,371
Product and content delivery expenses	9,475	36,781
Other expenses	130	530
Gross contribution	$ 7,577	$ 18,576