Operating Segments - Schedule of Information by Reportable Segment (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Segment Reporting Information [Line Items]
Total revenues	$ 100,077	$ 113,670
Segment expenses	(45,097)	(49,491)
Selling, marketing, administrative and other expenses	(55,134)	(64,664)
Amortization of intangible assets	(2,514)	(3,066)
Restructuring costs	(6,624)	(1,589)
Interest expense and other income	512	(243)
Loss before income taxes	(8,780)	(5,383)
Research Segment [Member]
Segment Reporting Information [Line Items]
Total revenues	81,224	88,825
Segment expenses	(33,514)	(35,507)
Consulting Segment Member
Segment Reporting Information [Line Items]
Total revenues	18,498	23,831
Segment expenses	(10,097)	(12,353)
Events Segment [Member]
Segment Reporting Information [Line Items]
Total revenues	355	1,014
Segment expenses	(1,486)	(1,631)
Research [Member]
Segment Reporting Information [Line Items]
Total revenues	76,581	80,906
Research [Member] | Research Segment [Member]
Segment Reporting Information [Line Items]
Total revenues	76,581	80,906
Research [Member] | Consulting Segment Member
Segment Reporting Information [Line Items]
Total revenues	0	0
Research [Member] | Events Segment [Member]
Segment Reporting Information [Line Items]
Total revenues	0	0
Consulting [Member]
Segment Reporting Information [Line Items]
Total revenues	23,141	31,750
Consulting [Member] | Research Segment [Member]
Segment Reporting Information [Line Items]
Total revenues	4,643	7,919
Consulting [Member] | Consulting Segment Member
Segment Reporting Information [Line Items]
Total revenues	18,498	23,831
Consulting [Member] | Events Segment [Member]
Segment Reporting Information [Line Items]
Total revenues	0	0
Events [Member]
Segment Reporting Information [Line Items]
Total revenues	355	1,014
Events [Member] | Research Segment [Member]
Segment Reporting Information [Line Items]
Total revenues	0	0
Events [Member] | Consulting Segment Member
Segment Reporting Information [Line Items]
Total revenues	0	0
Events [Member] | Events Segment [Member]
Segment Reporting Information [Line Items]
Total revenues	$ 355	$ 1,014