Goodwill and Intangible Assets - Schedule of Goodwill (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Goodwill [Roll Forward]
Beginning Balance	$ 740,955	$ 835,935
Acquired goodwill	1,025	37,592
Impairment loss recognized	(4,099)	(74,560)
Transfer of goodwill between segments	0	0
Transfer of goodwill to asset held for sale	0	(45,224)
Foreign currency translation	2,793	(12,788)
Ending Balance	740,674	740,955
Media Services
Goodwill [Roll Forward]
Beginning Balance	111,346	160,057
Acquired goodwill	0	0
Impairment loss recognized	0	(52,041)
Transfer of goodwill between segments	(24,119)	3,773
Transfer of goodwill to asset held for sale	0	0
Foreign currency translation	0	(443)
Ending Balance	87,227	111,346
All Other [Domain]
Goodwill [Roll Forward]
Beginning Balance	154,171	201,121
Acquired goodwill	1,025	32,776
Impairment loss recognized	(4,099)	(4,691)
Transfer of goodwill between segments	(4,206)	(22,920)
Transfer of goodwill to asset held for sale	0	(45,224)
Foreign currency translation	1,440	(6,891)
Ending Balance	148,331	154,171
Global Integrated Agencies
Goodwill [Roll Forward]
Beginning Balance	353,155	359,071
Acquired goodwill	0	0
Impairment loss recognized	0	(17,828)
Transfer of goodwill between segments	(85,766)	17,081
Transfer of goodwill to asset held for sale	0	0
Foreign currency translation	775	(5,169)
Ending Balance	268,164	353,155
Domestic Creative Agencies
Goodwill [Roll Forward]
Beginning Balance	38,780	36,980
Acquired goodwill	0	0
Impairment loss recognized	0	0
Transfer of goodwill between segments	119,097	2,066
Transfer of goodwill to asset held for sale	0	0
Foreign currency translation	402	(266)
Ending Balance	158,279	38,780
Specialist Communications [Member]
Goodwill [Roll Forward]
Beginning Balance	83,503	78,706
Acquired goodwill	0	4,816
Impairment loss recognized	0	0
Transfer of goodwill between segments	(5,006)	0
Transfer of goodwill to asset held for sale	0	0
Foreign currency translation	176	(19)
Ending Balance	$ 78,673	$ 83,503