Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Disaggregation of Revenue [Line Items]
Revenues	$ 663,791	$ 466,634	$ 1,979,607	$ 857,436
United States
Disaggregation of Revenue [Line Items]
Revenues	553,744	387,662	1,650,610	733,038
United Kingdom
Disaggregation of Revenue [Line Items]
Revenues	42,774	32,218	125,950	62,416
Other
Disaggregation of Revenue [Line Items]
Revenues	67,273	46,754	203,047	61,982
Digital Transformation
Disaggregation of Revenue [Line Items]
Revenues	197,337	124,268	606,061	256,966
Creativity and Communications
Disaggregation of Revenue [Line Items]
Revenues	304,048	208,424	890,692	261,080
Performance Media and Data
Disaggregation of Revenue [Line Items]
Revenues	111,548	88,139	325,584	222,186
Consumer Insights and Strategy
Disaggregation of Revenue [Line Items]
Revenues	$ 50,858	$ 45,803	$ 157,270	$ 117,204