Operating Segments - Schedule of Information about Reportable Segments, Disaggregation of Revenue by Product (Detail) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Segment Reporting Information [Line Items]
Total revenues	$ 106,345	$ 100,649
Segment expenses	(38,162)	(40,345)
Selling, marketing, administrative and other expenses	(59,875)	(62,011)
Amortization of intangible assets	(4,712)	(6,210)
Acquisition and integration costs	(2,875)	(2,967)
Interest expense, other income and gain (loss) on investments	(1,215)	(2,658)
Loss before income taxes	(494)	(13,542)
Products Segment [Member]
Segment Reporting Information [Line Items]
Total revenues	39,918	37,967
Segment expenses	(19,378)	(19,948)
Research Segment [Member]
Segment Reporting Information [Line Items]
Total revenues	66,427	62,682
Segment expenses	(18,784)	(20,397)
Research [Member]
Segment Reporting Information [Line Items]
Total revenues	53,606	49,780
Research [Member] \| Research Segment [Member]
Segment Reporting Information [Line Items]
Total revenues	53,606	49,780
Connect [Member]
Segment Reporting Information [Line Items]
Total revenues	13,889	13,571
Connect [Member] \| Products Segment [Member]
Segment Reporting Information [Line Items]
Total revenues	13,889	13,571
Analytics [Member]
Segment Reporting Information [Line Items]
Total revenues	5,301	5,258
Analytics [Member] \| Products Segment [Member]
Segment Reporting Information [Line Items]
Total revenues	5,301	5,258
Research Services [Member]
Segment Reporting Information [Line Items]
Total revenues	72,796	68,609
Research Services [Member] \| Products Segment [Member]
Segment Reporting Information [Line Items]
Total revenues	19,190	18,829
Research Services [Member] \| Research Segment [Member]
Segment Reporting Information [Line Items]
Total revenues	53,606	49,780
Consulting [Member]
Segment Reporting Information [Line Items]
Total revenues	33,459	31,787
Consulting [Member] \| Products Segment [Member]
Segment Reporting Information [Line Items]
Total revenues	20,638	18,885
Consulting [Member] \| Research Segment [Member]
Segment Reporting Information [Line Items]
Total revenues	12,821	12,902
Events [Member]
Segment Reporting Information [Line Items]
Total revenues	90	253
Events [Member] \| Products Segment [Member]
Segment Reporting Information [Line Items]
Total revenues	90	253
Advisory Services and Events [Member]
Segment Reporting Information [Line Items]
Total revenues	33,549	32,040
Advisory Services and Events [Member] \| Products Segment [Member]
Segment Reporting Information [Line Items]
Total revenues	20,728	19,138
Advisory Services and Events [Member] \| Research Segment [Member]
Segment Reporting Information [Line Items]
Total revenues	$ 12,821	$ 12,902

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Amount of income (loss) from continuing operations, including income (loss) from equity method investments, before deduction of income tax expense (benefit), and income (loss) attributable to noncontrolling interest.

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Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

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The aggregate total costs related to selling a firm's product and services, as well as all other general and administrative expenses. Direct selling expenses (for example, credit, warranty, and advertising) are expenses that can be directly linked to the sale of specific products. Indirect selling expenses are expenses that cannot be directly linked to the sale of specific products, for example telephone expenses, Internet, and postal charges. General and administrative expenses include salaries of non-sales personnel, rent, utilities, communication, etc.

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