Segment Information (Details) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) reportable_segment	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | reportable_segment			4
Revenue	$ 375,800	$ 349,254	$ 1,111,032	$ 995,343
Cost of services sold	249,418	235,659	754,803	675,940
Office and general expenses	77,910	83,303	251,313	233,840
Depreciation, Depletion, Amortization and Impairment, Nonproduction	11,252	41,043	32,916	63,699
Operating profit	37,220	(10,751)	72,000	21,864
Other Income (Expense):
Other income, net	8,649	(6,008)	17,812	9,530
Interest and Debt Expense, net	16,258	16,322	48,309	48,690
Gain (Loss) on Repurchase of Debt Instrument	0	0	0	(33,298)
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	29,611	(33,081)	41,503	(50,594)
Income Tax Expense (Benefit)	9,049	(1,930)	17,659	1,180
Income Loss From Continuing Operations Before Equity In Earnings Of Non-consolidated Affiliates	20,562	(31,151)	23,844	(51,774)
Income (Loss) from Equity Method Investments	1,422	70	1,924	9
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	21,984	(31,081)	25,768	(51,765)
Net Income (Loss) Attributable to Noncontrolling Interest	(3,491)	(1,059)	(6,588)	(3,172)	$ (5,218)
Net Income (Loss) Attributable to Parent	18,493	(32,140)	19,180	(54,937)
Stock-based compensation	6,380	5,228	16,870	15,443
Supplemental Segment Information:
Capital expenditures	7,149	6,274	28,305	19,723
Total Assets	1,617,831		1,617,831		$ 1,577,378
Corporate [Member]
Segment Reporting Information [Line Items]
Depreciation, Depletion, Amortization and Impairment, Nonproduction	255	359	864	1,266
Operating profit	(10,724)	(7,051)	(28,982)	(32,982)
Other Income (Expense):
Stock-based compensation	477	605	1,599	2,059
Supplemental Segment Information:
Capital expenditures	1	0	4	32
Global Integrated Agencies [Member]
Segment Reporting Information [Line Items]
Revenue	193,979	177,262	576,935	489,880
Depreciation, Depletion, Amortization and Impairment, Nonproduction	6,359	6,111	17,889	14,986
Operating profit	19,819	2,873	33,765	24,316
Other Income (Expense):
Net Income (Loss) Attributable to Parent	18,493	(32,140)	19,180	(54,937)
Stock-based compensation	3,840	2,890	9,892	9,030
Supplemental Segment Information:
Capital expenditures	1,950	3,003	17,639	10,703
Domestic Creative Agencies [Member]
Segment Reporting Information [Line Items]
Revenue	24,173	22,181	67,473	66,274
Depreciation, Depletion, Amortization and Impairment, Nonproduction	336	353	1,062	1,263
Operating profit	5,716	4,688	13,563	14,779
Other Income (Expense):
Stock-based compensation	177	150	502	487
Supplemental Segment Information:
Capital expenditures	324	222	874	920
Specialized Communications [Member]
Segment Reporting Information [Line Items]
Revenue	40,670	40,309	125,470	123,006
Depreciation, Depletion, Amortization and Impairment, Nonproduction	1,220	189	3,657	5,123
Operating profit	4,775	11,101	13,410	17,860
Other Income (Expense):
Stock-based compensation	659	564	2,264	1,556
Supplemental Segment Information:
Capital expenditures	206	56	673	2,183
Media Services [Member]
Segment Reporting Information [Line Items]
Revenue	33,027	34,481	103,966	96,681
Depreciation, Depletion, Amortization and Impairment, Nonproduction	917	2,338	2,933	4,437
Operating profit	2,421	466	8,618	3,510
Other Income (Expense):
Stock-based compensation	150	70	464	187
Supplemental Segment Information:
Capital expenditures	2,171	2,008	3,455	2,634
All Other [Member]
Segment Reporting Information [Line Items]
Revenue	83,951	75,021	237,188	219,502
Depreciation, Depletion, Amortization and Impairment, Nonproduction	2,165	31,693	6,511	36,624
Operating profit	15,213	(22,828)	31,626	(5,619)
Other Income (Expense):
Stock-based compensation	1,077	949	2,149	2,124
Supplemental Segment Information:
Capital expenditures	2,497	985	5,660	3,251
CANADA
Segment Reporting Information [Line Items]
Revenue	31,418	30,233	88,471	92,253
Other Regions [Member]
Segment Reporting Information [Line Items]
Revenue	54,680	44,515	153,714	103,394
UNITED STATES
Segment Reporting Information [Line Items]
Revenue	$ 289,702	$ 274,506	$ 868,847	$ 799,696