Business Acquisitions - Narrative (Details) $ in Thousands		12 Months Ended
	Jun. 04, 2021 USD ($)	Dec. 31, 2023 USD ($) acquisition	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($) acquisition
Business Acquisition [Line Items]
Goodwill		$ 1,546,065	$ 1,591,474	$ 1,531,455
Increase (decrease) in goodwill from adjustment under purchase accounting		(72)	$ 4,338
Fiscal 2023 Acquisitions
Business Acquisition [Line Items]
Goodwill		6,500
Definite-lived intangibles in connection with acquisition		7,200
Increase (decrease) in goodwill from adjustment under purchase accounting		(100)
Lifecycle Marketing Group Limited
Business Acquisition [Line Items]
Equity interest acquired (percentage)			100.00%
FitNow, Inc.
Business Acquisition [Line Items]
Equity interest acquired (percentage)			100.00%
Fiscal 2022 Acquisitions
Business Acquisition [Line Items]
Goodwill			$ 95,737
Increase (decrease) in goodwill from adjustment under purchase accounting			4,500
Revenue of acquiree since acquisition date			33,000
Total consideration of transactions			121,700
Fair value of assets		$ 7,400
Expected income tax deductible amount			1,200
Goodwill, increase (decrease) in connection with contract liability			$ 3,200
Unfavorable contract liability, accretion period			3 years
Accounts receivable			$ 7,433
Fiscal 2022 Acquisitions | Cybersecurity and Martech
Business Acquisition [Line Items]
Increase (decrease) in goodwill from adjustment under purchase accounting			$ (100)
Series of Individually Immaterial Business Acquisitions
Business Acquisition [Line Items]
Number of immaterial acquisitions | acquisition		2		4
Fiscal 2021 Acquisitions
Business Acquisition [Line Items]
Goodwill				$ 97,032
Total consideration of transactions				160,400
Fair value of assets				9,500
Expected income tax deductible amount				42,100
Revenues contributed through acquisitions				39,900
Gross amount due under contracts				9,900
Amount expected to be uncollectible				400
Accounts receivable				9,513
SEOmoz Acquisition
Business Acquisition [Line Items]
Goodwill	$ 41,329			41,300
Total consideration of transactions	67,000
Expected income tax deductible amount				0
Revenues contributed through acquisitions				$ 25,600
Gross amount due under contracts	3,600
Amount expected to be uncollectible	300
Accounts receivable	$ 3,278