Segment Information (Details 1) $ in Thousands	3 Months Ended				6 Months Ended	7 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2023 USD ($)	Sep. 30, 2023 USD ($)	Jun. 30, 2023 USD ($)	Mar. 31, 2023 USD ($)	Jun. 30, 2023 USD ($)	Aug. 02, 2021 USD ($)	Sep. 30, 2023 USD ($)	Dec. 31, 2023 USD ($) reportable_segment	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | reportable_segment								3
Revenues	$ 654,895	$ 617,573	$ 632,265	$ 622,444				$ 2,527,177	$ 2,687,792	$ 1,469,363
Adjusted EBITDA								(360,139)	(451,118)	(253,652)
Depreciation, Depletion and Amortization, Nonproduction								(142,831)	(131,273)	(77,503)
Asset Impairment Charges								(11,395)	(122,179)	(16,240)
Stock-based compensation								(57,179)	(33,152)	(75,032)
Deferred Acquisition Consideration Expense (Income)								(13,060)	13,405	(18,721)
Other items, net								(45,147)	(18,691)	(21,430)
Operating income								90,527	159,228	44,726
Interest and Debt Expense								(90,644)	(76,062)	(31,894)
Foreign exchange, net								(2,960)	(2,606)	(3,332)
Other Nonoperating Income (Expense)								(359)	(4,975)	7,020
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest								91,069	75,585	59,558
Income tax expense	35,560	4,324	437	236	$ 673		$ 4,997	40,557	25,462	23,398
Income Loss From Continuing Operations Before Equity In Earnings Of Non-consolidated Affiliates	54,782	3,121	(4,749)	(2,642)	(7,391)		(4,270)	50,512	50,123	36,160
Income (Loss) from Equity Method Investments								(8,870)	(79)	(240)
Net Income (Loss), Including Portion Attributable to Nonredeemable Noncontrolling Interest	46,359	3,117	(4,965)	(2,869)	(7,834)		(4,717)	41,642	50,044	35,920
Net Income (Loss) Attributable to Noncontrolling Interest	(45,073)	(2,464)	1,771	4,258	6,029	$ (39,626)	3,565	(41,508)	(30,125)	(14,884)
Net Income (Loss) Attributable to Parent	1,286	$ 653	$ (3,194)	$ 1,389	$ (1,805)		$ (1,152)	134	19,919	21,036
Long-Lived Assets	332,100							332,100	372,400
UNITED STATES
Segment Reporting Information [Line Items]
Revenues								2,048,229	2,218,681	1,219,816
Long-Lived Assets	268,500							268,500	315,800
All other countries
Segment Reporting Information [Line Items]
Long-Lived Assets	$ 63,600							63,600	56,700
Operating Segments | Integrated Agencies Network
Segment Reporting Information [Line Items]
Revenues								1,378,109	1,474,970	771,123
Adjusted EBITDA								(271,322)	(292,293)	(165,385)
Operating Segments | Brand Performance Network
Segment Reporting Information [Line Items]
Revenues								768,776	757,208	424,632
Adjusted EBITDA								(96,015)	(115,835)	(65,942)
Operating Segments | Communications Network
Segment Reporting Information [Line Items]
Revenues								333,707	435,652	247,766
Adjusted EBITDA								(51,819)	(87,032)	(43,741)
Operating Segments | All Other
Segment Reporting Information [Line Items]
Revenues								46,585	19,962	25,842
Adjusted EBITDA								(10,607)	(931)	772
Corporate, Non-Segment
Segment Reporting Information [Line Items]
Adjusted EBITDA								$ 48,410	$ 43,111	$ 20,644