Goodwill and Intangible Assets - Schedule of Goodwill (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Goodwill [Roll Forward]
Beginning Balance	$ 351,725	$ 325,185
Acquired goodwill	1,303,649	23,775
Disposition	(935)
Foreign currency translation	(1,716)	2,765
Ending Balance	1,652,723	351,725
Corporate, Non-Segment
Goodwill [Roll Forward]
Beginning Balance	0	0
Acquired goodwill	0
Disposition	0
Foreign currency translation	0	0
Ending Balance	0	0
Integrated Agencies Network | Operating Segments
Goodwill [Roll Forward]
Beginning Balance	95,164	88,094
Acquired goodwill	1,058,411	7,070
Disposition	0
Foreign currency translation	(502)	0
Ending Balance	1,153,073	95,164
Media Network | Operating Segments
Goodwill [Roll Forward]
Beginning Balance	180,639	177,073
Acquired goodwill	178,994	235
Disposition	0
Foreign currency translation	(1,020)	3,331
Ending Balance	358,613	180,639
Communication Network | Operating Segments
Goodwill [Roll Forward]
Beginning Balance	49,533	33,258
Acquired goodwill	66,244	16,275
Disposition	0
Foreign currency translation	0	0
Ending Balance	115,777	49,533
All Other | Operating Segments
Goodwill [Roll Forward]
Beginning Balance	26,389	26,760
Acquired goodwill	0	195
Disposition	(935)
Foreign currency translation	(194)	(566)
Ending Balance	$ 25,260	$ 26,389