Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Disaggregation of Revenue [Line Items]
Revenues	$ 672,913	$ 209,560	$ 1,315,816	$ 390,802
United States
Disaggregation of Revenue [Line Items]
Revenues	559,635	183,358	1,096,866	350,105
United Kingdom
Disaggregation of Revenue [Line Items]
Revenues	43,363	12,070	83,176	16,775
Other
Disaggregation of Revenue [Line Items]
Revenues	69,915	14,132	135,774	23,922
Digital Transformation
Disaggregation of Revenue [Line Items]
Revenues	197,915	70,261	408,724	132,698
Creativity and Communications
Disaggregation of Revenue [Line Items]
Revenues	307,402	27,986	586,644	52,656
Performance Media and Data
Disaggregation of Revenue [Line Items]
Revenues	114,260	71,439	214,036	134,047
Consumer Insights and Strategy
Disaggregation of Revenue [Line Items]
Revenues	$ 53,336	$ 39,874	$ 106,412	$ 71,401