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Interest expense, other income (expense) and gains (losses) on investments.

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The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

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The aggregate cost of goods produced and sold and services rendered during the reporting period.

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Aggregate revenue less cost of goods and services sold or operating expenses directly attributable to the revenue generation activity.

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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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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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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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Operating Segment and Enterprise Wide Reporting - Schedule of Information about Reportable Segments, Disaggregation of Revenue by Product (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Total revenues	$ 124,269	$ 108,596	$ 128,183	$ 100,649	$ 98,583	$ 84,890	$ 96,353	$ 77,749	$ 461,697	$ 357,575	$ 337,673
Segment expenses									182,584	128,365	118,711
Contribution margin									279,113	229,210	218,962
Selling, marketing, administrative and other expenses									(248,621)	(201,836)	(190,632)
Amortization of intangible assets									(22,619)	(1,162)	(781)
Acquisition and integration costs									(8,948)	(3,787)
Interest expense, other income (expense) and gains (losses) on investments									(8,524)	1,100	(178)
Income (loss) before income taxes									(9,599)	23,525	27,371
Research [Member]
Segment Reporting Information [Line Items]
Total revenues									219,189	157,112	148,935
Connect [Member]
Segment Reporting Information [Line Items]
Total revenues									56,224	51,377	48,798
Analytics [Member]
Segment Reporting Information [Line Items]
Total revenues									23,322	19,910	18,738
Research Services [Member]
Segment Reporting Information [Line Items]
Total revenues									298,735	228,399	216,471
Consulting [Member]
Segment Reporting Information [Line Items]
Total revenues									135,952	115,705	109,447
Events [Member]
Segment Reporting Information [Line Items]
Total revenues									27,010	13,471	11,755
Advisory Services and Events [Member]
Segment Reporting Information [Line Items]
Total revenues									162,962	129,176	121,202
Products Segment [Member]
Segment Reporting Information [Line Items]
Total revenues									167,224	149,067	143,374
Segment expenses									81,520	75,039	67,739
Contribution margin									85,704	74,028	75,635
Products Segment [Member] \| Connect [Member]
Segment Reporting Information [Line Items]
Total revenues									54,350	51,377	48,798
Products Segment [Member] \| Analytics [Member]
Segment Reporting Information [Line Items]
Total revenues									23,322	19,910	18,738
Products Segment [Member] \| Research Services [Member]
Segment Reporting Information [Line Items]
Total revenues									77,672	71,287	67,536
Products Segment [Member] \| Consulting [Member]
Segment Reporting Information [Line Items]
Total revenues									76,567	64,309	64,083
Products Segment [Member] \| Events [Member]
Segment Reporting Information [Line Items]
Total revenues									12,985	13,471	11,755
Products Segment [Member] \| Advisory Services and Events [Member]
Segment Reporting Information [Line Items]
Total revenues									89,552	77,780	75,838
Research Segment [Member]
Segment Reporting Information [Line Items]
Total revenues									214,745	208,508	194,299
Segment expenses									55,330	53,326	50,972
Contribution margin									159,415	155,182	143,327
Research Segment [Member] \| Research [Member]
Segment Reporting Information [Line Items]
Total revenues									161,487	157,112	148,935
Research Segment [Member] \| Research Services [Member]
Segment Reporting Information [Line Items]
Total revenues									161,487	157,112	148,935
Research Segment [Member] \| Consulting [Member]
Segment Reporting Information [Line Items]
Total revenues									53,258	51,396	45,364
Research Segment [Member] \| Advisory Services and Events [Member]
Segment Reporting Information [Line Items]
Total revenues									53,258	$ 51,396	$ 45,364
Sirius Decisions Segment [Member]
Segment Reporting Information [Line Items]
Total revenues									79,728
Segment expenses									45,734
Contribution margin									33,994
Sirius Decisions Segment [Member] \| Research [Member]
Segment Reporting Information [Line Items]
Total revenues									57,702
Sirius Decisions Segment [Member] \| Connect [Member]
Segment Reporting Information [Line Items]
Total revenues									1,874
Sirius Decisions Segment [Member] \| Research Services [Member]
Segment Reporting Information [Line Items]
Total revenues									59,576
Sirius Decisions Segment [Member] \| Consulting [Member]
Segment Reporting Information [Line Items]
Total revenues									6,127
Sirius Decisions Segment [Member] \| Events [Member]
Segment Reporting Information [Line Items]
Total revenues									14,025
Sirius Decisions Segment [Member] \| Advisory Services and Events [Member]
Segment Reporting Information [Line Items]
Total revenues									$ 20,152