Operating Segments - Schedule of Information by Reportable Segment (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Segment Reporting Information [Line Items]
Total revenues	$ 113,670	$ 124,971
Segment expenses	49,491	50,248
Selling, marketing, administrative and other expenses	(64,664)	(64,890)
Amortization of intangible assets	(3,066)	(3,362)
Restructuring costs	(1,589)	0
Interest expense, other income (expense), and gains on investments	243	(444)
Income (Loss) before income taxes	(5,383)	6,027
Research Segment [Member]
Segment Reporting Information [Line Items]
Total revenues	88,825	96,970
Segment expenses	35,507	34,180
Consulting Segment Member
Segment Reporting Information [Line Items]
Total revenues	23,831	27,241
Segment expenses	12,353	14,317
Events Segment [Member]
Segment Reporting Information [Line Items]
Total revenues	1,014	760
Segment expenses	1,631	1,751
Research [Member]
Segment Reporting Information [Line Items]
Total revenues	80,906	85,780
Research [Member] | Research Segment [Member]
Segment Reporting Information [Line Items]
Total revenues	80,906	85,780
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	31,750	38,431
Consulting [Member] | Research Segment [Member]
Segment Reporting Information [Line Items]
Total revenues	7,919	11,190
Consulting [Member] | Consulting Segment Member
Segment Reporting Information [Line Items]
Total revenues	23,831	27,241
Consulting [Member] | Events Segment [Member]
Segment Reporting Information [Line Items]
Total revenues	0	0
Events [Member]
Segment Reporting Information [Line Items]
Total revenues	1,014	760
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	$ 1,014	$ 760