Operating Segments - Schedule of Information by Reportable Segment (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2025		Mar. 31, 2024
Segment Reporting Information [Line Items]
Total revenues	$ 89,876		$ 100,077
Loss from operations	(87,591)		(9,292)
Selling, marketing, administrative and other expenses	(54,049)		(56,623)
Amortization of intangible assets	(2,217)		(2,514)
Goodwill impairment	(83,895)		0
Restructuring and related costs	(1,507)		(6,624)
Interest expense and other income			512
Interest expense, other income and loss on investments	(711)
Loss before income taxes	(88,302)		(8,780)
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	89,876		100,077
Segment expenses	(35,799)	[1]	(43,608)	[2]
Loss from operations	54,077		56,469
Research Segment [Member]
Segment Reporting Information [Line Items]
Goodwill impairment	(83,895)
Research Segment [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	73,472		81,224
Segment expenses	(26,136)	[1]	(31,944)	[2]
Loss from operations	47,336		49,280
Consulting Segment Member
Segment Reporting Information [Line Items]
Goodwill impairment	0
Consulting Segment Member | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	16,378		18,498
Segment expenses	(8,899)	[1]	(10,886)	[2]
Loss from operations	7,479		7,612
Events Segment [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	26		355
Segment expenses	(764)	[1]	(778)	[2]
Loss from operations	(738)		(423)
Research [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	68,414		76,581
Research [Member] | Research Segment [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	68,414		76,581
Research [Member] | Consulting Segment Member | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	0		0
Research [Member] | Events Segment [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	0		0
Consulting [Member]
Segment Reporting Information [Line Items]
Total revenues	21,436		23,141
Consulting [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	21,436		23,141
Consulting [Member] | Research Segment [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	5,058		4,643
Consulting [Member] | Consulting Segment Member | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	16,378		18,498
Consulting [Member] | Events Segment [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	0		0
Events [Member]
Segment Reporting Information [Line Items]
Total revenues	26		355
Events [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	26		355
Events [Member] | Research Segment [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	0		0
Events [Member] | Consulting Segment Member | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	0		0
Events [Member] | Events Segment [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	26		355
Compensation Benefits and Related Costs [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Segment expenses	(30,186)	[1]	(36,416)	[2]
Compensation Benefits and Related Costs [Member] | Research Segment [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Segment expenses	(22,552)	[1]	(27,263)	[2]
Compensation Benefits and Related Costs [Member] | Consulting Segment Member | Operating Segments [Member]
Segment Reporting Information [Line Items]
Segment expenses	(6,907)	[1]	(8,380)	[2]
Compensation Benefits and Related Costs [Member] | Events Segment [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Segment expenses	(727)	[1]	(773)	[2]
Professional Services [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Segment expenses	(3,205)	[1]	(4,132)	[2]
Professional Services [Member] | Research Segment [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Segment expenses	(2,691)	[1]	(3,651)	[2]
Professional Services [Member] | Consulting Segment Member | Operating Segments [Member]
Segment Reporting Information [Line Items]
Segment expenses	(513)	[1]	(478)	[2]
Professional Services [Member] | Events Segment [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Segment expenses	(1)	[1]	(3)	[2]
Billable Expenses [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Segment expenses	(1,440)	[1]	(2,088)	[2]
Billable Expenses [Member] | Research Segment [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Segment expenses	(83)	[1]	(148)	[2]
Billable Expenses [Member] | Consulting Segment Member | Operating Segments [Member]
Segment Reporting Information [Line Items]
Segment expenses	(1,357)	[1]	(1,940)	[2]
Billable Expenses [Member] | Events Segment [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Segment expenses	0	[1]	0	[2]
Travel and Entertainment [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Segment expenses	(505)	[1]	(388)	[2]
Travel and Entertainment [Member] | Research Segment [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Segment expenses	(389)	[1]	(299)	[2]
Travel and Entertainment [Member] | Consulting Segment Member | Operating Segments [Member]
Segment Reporting Information [Line Items]
Segment expenses	(112)	[1]	(84)	[2]
Travel and Entertainment [Member] | Events Segment [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Segment expenses	(4)	[1]	(5)	[2]
Software [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Segment expenses	(394)	[1]	(462)	[2]
Software [Member] | Research Segment [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Segment expenses	(377)	[1]	(458)	[2]
Software [Member] | Consulting Segment Member | Operating Segments [Member]
Segment Reporting Information [Line Items]
Segment expenses	0	[1]	0	[2]
Software [Member] | Events Segment [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Segment expenses	(17)	[1]	(4)	[2]
Other Segment Expenses [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Segment expenses	(69)	[1],[3]	(122)	[2],[4]
Other Segment Expenses [Member] | Research Segment [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Segment expenses	(44)	[1],[3]	(125)	[2],[4]
Other Segment Expenses [Member] | Consulting Segment Member | Operating Segments [Member]
Segment Reporting Information [Line Items]
Segment expenses	(10)	[1],[3]	(4)	[2],[4]
Other Segment Expenses [Member] | Events Segment [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Segment expenses	$ (15)	[1],[3]	$ 7	[2],[4]

[1] The significant expense categories and amounts align with the segment-level information that is regularly provided to the chief operating decision maker.

[2] The significant expense categories and amounts align with the segment-level information that is regularly provided to the chief operating decision maker.

[3] Other segment expenses for each reportable segment includes office supplies, maintenance, and training expenses.

[4] Other segment expenses for each reportable segment includes office supplies, maintenance, and training expenses.