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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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Describes the event or transaction that occurred between the balance sheet date and the date the financial statements are issued or available to be issued.

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No definition available.

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Date the event occurred after the balance sheet date but before financial statements are issues or available to be issued, in CCYY-MM-DD format.

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Subsequent Events - Additional Information (Detail) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
	Mar. 13, 2020	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
Subsequent Event [Line Items]
Revenue		$ 124,269	$ 108,596	$ 128,183	$ 100,649	$ 98,583	$ 84,890	$ 96,353	$ 77,749	$ 461,697	$ 357,575	$ 337,673
Income (loss) from operations		$ 6,827	$ (1,640)	$ 4,622	$ (10,884)	$ 8,744	$ 4,942	$ 11,027	$ (2,288)	$ (1,075)	$ 22,425	$ 27,549
Subsequent Event [Member] \| Summit Update [Member]
Subsequent Event [Line Items]
Subsequent event, date	Mar. 13, 2020
Description of subsequent event	Due to considerations of the effect of the novel coronavirus, the Company announced on March 13, 2020 that it will be holding its SiriusDecisions Summit 2020, its single largest event, as a virtual event during its originally scheduled timeframe in May 2020. The Company estimates the impact of holding the event as a virtual event, as compared to a live event, will reduce revenues by $7.0 million to $9.0 million and will reduce operating income by $4.0 million to $6.0 million.
Subsequent Event [Member] \| Minimum [Member] \| Summit Update [Member]
Subsequent Event [Line Items]
Revenue	$ 7,000
Income (loss) from operations	4,000
Subsequent Event [Member] \| Maximum [Member] \| Summit Update [Member]
Subsequent Event [Line Items]
Revenue	9,000
Income (loss) from operations	$ 6,000