Goodwill and Intangible Assets - Schedule of Goodwill (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Goodwill [Roll Forward]
Beginning Balance	$ 870,301,000	$ 851,373,000
Acquired goodwill	24,778,000	43,654,000
Goodwill, Impairment Loss	(764,000)		$ (15,564)
Goodwill, Purchase Accounting Adjustments		(2,428,000)
Goodwill, Impairment Loss	(48,524,000)	0	0
Goodwill, Transfers	0
Foreign currency translation	(1,032,000)	(22,298,000)
Ending Balance	844,759,000	870,301,000	851,373,000
Reportable Segment [Domain]
Goodwill [Roll Forward]
Beginning Balance	142,286,000	136,033,000
Acquired goodwill	0	6,253,000
Goodwill, Impairment Loss	0
Goodwill, Purchase Accounting Adjustments		0
Goodwill, Impairment Loss	0
Goodwill, Transfers	34,400,000
Foreign currency translation	0	0
Ending Balance	176,686,000	142,286,000	136,033,000
All Other [Domain]
Goodwill [Roll Forward]
Beginning Balance	229,607,000	209,632,000
Acquired goodwill	0	37,401,000
Goodwill, Impairment Loss	(764,000)
Goodwill, Purchase Accounting Adjustments		(684,000)
Goodwill, Impairment Loss	(29,631,000)
Goodwill, Transfers	0
Foreign currency translation	2,692,000	(16,742,000)
Ending Balance	201,904,000	229,607,000	209,632,000
Global Integrated Agencies [Member]
Goodwill [Roll Forward]
Beginning Balance	364,159,000	370,094,000
Acquired goodwill	24,778,000	0
Goodwill, Impairment Loss	0
Goodwill, Purchase Accounting Adjustments		(998,000)
Goodwill, Impairment Loss	0
Goodwill, Transfers	(34,400,000)
Foreign currency translation	(3,821,000)	(4,937,000)
Ending Balance	350,716,000	364,159,000	370,094,000
Domestic Creative Agencies [Member]
Goodwill [Roll Forward]
Beginning Balance	36,671,000	37,117,000
Acquired goodwill	0	0
Goodwill, Impairment Loss	0
Goodwill, Purchase Accounting Adjustments		133,000
Goodwill, Impairment Loss	0
Goodwill, Transfers	0
Foreign currency translation	91,000	(579,000)
Ending Balance	36,762,000	36,671,000	37,117,000
Specialist Communications [Member]
Goodwill [Roll Forward]
Beginning Balance	97,578,000	98,497,000
Acquired goodwill	0	0
Goodwill, Impairment Loss	0
Goodwill, Purchase Accounting Adjustments		(879,000)
Goodwill, Impairment Loss	(18,893,000)
Goodwill, Transfers	0
Foreign currency translation	6,000	(40,000)
Ending Balance	$ 78,691,000	$ 97,578,000	$ 98,497,000