Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Disaggregation of Revenue [Line Items]
Revenues	$ 622,444	$ 642,903
United States
Disaggregation of Revenue [Line Items]
Revenues	507,092	537,231
United Kingdom
Disaggregation of Revenue [Line Items]
Revenues	41,271	39,813
Other
Disaggregation of Revenue [Line Items]
Revenues	74,081	65,859
Digital Transformation
Disaggregation of Revenue [Line Items]
Revenues	190,319	210,809
Creativity and Communications
Disaggregation of Revenue [Line Items]
Revenues	261,354	279,242
Performance Media and Data
Disaggregation of Revenue [Line Items]
Revenues	109,488	99,776
Consumer Insights and Strategy
Disaggregation of Revenue [Line Items]
Revenues	$ 61,283	$ 53,076