Segment Information (Details 1) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($) reportable_segment	Sep. 30, 2022 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | reportable_segment			3
Revenues	$ 617,573	$ 663,791	$ 1,872,282	$ 1,979,607
Adjusted EBITDA	(101,769)	(115,092)	(265,159)	(327,823)
Depreciation, Depletion and Amortization, Nonproduction	(38,830)	(32,207)	(107,795)	(95,642)
Asset Impairment Charges	0	(25,211)	(10,562)	(28,034)
Stock-based compensation	(12,065)	(12,258)	(34,615)	(33,410)
Deferred Acquisition Consideration Expense (Income)	(6,401)	29,789	(10,881)	14,420
Other items, net	(10,731)	(5,152)	(30,069)	(12,112)
Operating income	33,742	70,053	71,237	173,045
Interest and Debt Expense	(25,886)	(19,672)	(67,755)	(56,552)
Foreign exchange, net	(140)	(3,927)	(2,288)	(4,163)
Other Nonoperating Income (Expense)	(271)	147	(467)	182
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	7,445	46,601	727	112,512
Income tax expense	4,324	11,540	12,425	20,150
Income Loss From Continuing Operations Before Equity In Earnings Of Non-consolidated Affiliates	3,121	35,061	(11,698)	92,362
Income (Loss) from Equity Method Investments	(4)	213	(447)	1,053
Net Income (Loss), Including Portion Attributable to Nonredeemable Noncontrolling Interest	3,117	35,274	(12,145)	93,415
Net Income (Loss) Attributable to Noncontrolling Interest	(2,464)	(24,665)	8,548	(59,668)
Net Income (Loss) Attributable to Parent	653	10,609	(3,597)	33,747
Operating Segments | Integrated Agencies Network
Segment Reporting Information [Line Items]
Revenues	348,781	366,437	1,032,914	1,092,364
Adjusted EBITDA	(77,177)	(76,198)	(211,377)	(215,462)
Operating Segments | Brand Performance Network
Segment Reporting Information [Line Items]
Revenues	173,361	171,463	574,729	563,546
Adjusted EBITDA	(23,193)	(24,312)	(67,387)	(89,259)
Operating Segments | Communications Network
Segment Reporting Information [Line Items]
Revenues	82,505	122,455	230,261	314,472
Adjusted EBITDA	(17,294)	(25,489)	(35,754)	(59,089)
Operating Segments | All Other
Segment Reporting Information [Line Items]
Revenues	12,926	3,436	34,378	9,225
Adjusted EBITDA	(4,005)	(363)	(10,166)	(972)
Corporate, Non-Segment
Segment Reporting Information [Line Items]
Adjusted EBITDA	$ 11,890	$ 10,544	$ 39,193	$ 35,015