Acquisitions (Details Textual) - USD ($)			3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2016	Jul. 01, 2016	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015	Apr. 01, 2016	Oct. 01, 2015	May 01, 2015
Business Acquisition [Line Items]
Business Acquisition, Pro Forma Revenue			$ 349,254,000	$ 341,268,000	$ 1,036,055,000	$ 1,017,492,000
Adjustments to deferred acquisition consideration included in share-based compensation			2,259	1,548	7,184	6,462
Goodwill, Acquired During Period					24,778,000		$ 43,655,000
Business Acquisition, Pro Forma Net Income (Loss)			(33,530,000)	(8,604,000)	(55,650,000)	(11,135,000)
Redeemable Noncontrolling Interest, Equity, Fair Value	$ 60,174,000		$ 60,174,000		$ 60,174,000		69,471,000
Noncontrolling Interest, Ownership Percentage by Parent	100.00%		100.00%		100.00%
Business Combination, Contingent Consideration, Liability	$ 243,097,000		$ 243,097,000		$ 243,097,000		347,104,000
Business Acquisition, Pro Forma Net Income (Loss)			$ (21,295,000)	$ (7,626,000)	$ (43,874,000)	$ (9,032,000)
Basic Earnings Per Share, Pro Forma			$ (410)	$ (150)	$ (840)	$ (170)
Diluted Earnings Per Share Pro Forma			$ (410)	$ (150)	$ (840)	$ (170)
Forsman & Bodenfors AB [Domain]
Business Acquisition [Line Items]
Business Acquisition, Pro Forma Revenue			$ 15,527
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles		$ 36,698
Goodwill, Acquired During Period		$ 24,778
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life		10 years 9 months
Business Combination, Acquisition of Less than 100 Percent, Redeemable Noncontrolling Interest, Fair Value		$ 2,275
Business Combination, Acquisition of Less than 100 Percent, Noncontrolling Interest, Fair Value		5,514
Business Acquisition, Goodwill, Expected Tax Deductible Amount		0
Deferred Taxes, Business Combination, Valuation Allowance, Available to Reduce Intangible Assets		$ 8,074
Business Acquisition, Pro Forma Revenue					$ 15,527
Business Acquisition, Pro Forma Net Income (Loss)					12,305
Business Acquisition, Percentage of Voting Interests Acquired		100.00%
Business Combination, Consideration Transferred		$ 49,837
Business Combination, Contingent Consideration, Liability	27,282	15,618	27,282		27,282
Business Acquisition, Pro Forma Net Income (Loss)			12,305
Luntz Global Partners L L C
Business Acquisition [Line Items]
Business Acquisition, Percentage of Voting Interests Acquired								40.00%
Aggregate 2016 Step Up Transactions [Member]
Business Acquisition [Line Items]
Business Acquisition, Cost of Acquired Entity, Cash Paid					1,089
Business Combination, Acquisition of Less than 100 Percent, Redeemable Noncontrolling Interest, Fair Value					182
Business Combinations, Assets Relinquished by Acquirer					428
Business Combinations, Liabilities Relinquished Previously due to Acquiree					44
Aggregate 2015 Acquisitions [Member]
Business Acquisition [Line Items]
Business Acquisition, Cost of Acquired Entity, Cash Paid							23,000
Business Combination, Consideration Transferred, Liabilities Incurred							32,279
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles							16,721
Goodwill, Acquired During Period							$ 43,654
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life							6 years 4 months
Business Acquisition, Goodwill, Expected Tax Deductible Amount							$ 9,720
Business Combination, Consideration Transferred							55,279
Aggregate 2015 Acquisitions [Member] | Y Media Labs, LLC [Member]
Business Acquisition [Line Items]
Business Combination, Acquisition of Less than 100 Percent, Noncontrolling Interest, Fair Value							1,999
Business Acquisition, Percentage of Voting Interests Acquired										60.00%
Aggregate 2015 Acquisitions [Member] | Unique Influence, LLC [Domain]
Business Acquisition [Line Items]
Business Acquisition, Percentage of Voting Interests Acquired									100.00%
Aggregate 2015 Step Up Transactions [Member]
Business Acquisition [Line Items]
Business Acquisition, Cost of Acquired Entity, Cash Paid							37,467
Business Combination, Consideration Transferred, Liabilities Incurred							163,355
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests							149,335
Business Combination, Consideration Transferred							200,822
Minimum [Member] | Forsman & Bodenfors AB [Domain]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred		35,000
Maximum [Member] | Forsman & Bodenfors AB [Domain]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred		$ 55,000
Noncontrolling Interest [Member]
Business Acquisition [Line Items]
Business Acquisition, Pro Forma Net Income (Loss)					0
Noncontrolling Interest [Member] | Aggregate 2015 Step Up Transactions [Member]
Business Acquisition [Line Items]
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests							8,708
Additional Paid-in Capital [Member]
Business Acquisition [Line Items]
Business Acquisition, Pro Forma Net Income (Loss)
Additional Paid-in Capital [Member] | Aggregate 2016 Step Up Transactions [Member]
Business Acquisition [Line Items]
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests					22,498
Additional Paid-in Capital [Member] | Aggregate 2015 Step Up Transactions [Member]
Business Acquisition [Line Items]
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests							42,780
Contingent payment [Domain]
Business Acquisition [Line Items]
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability			11,152,000	$ 4,928,000	17,180,000	$ (5,566,000)
Contingent payment [Domain] | Aggregate 2016 Step Up Transactions [Member]
Business Acquisition [Line Items]
Deferred Stock-based Compensation, Discounted					2,393
Business Combination, Consideration Transferred					4,052
Fixed payments [Member]
Business Acquisition [Line Items]
Business Combination, Contingent Consideration, Liability	4,790,000		$ 4,790,000		4,790,000		$ 40,370,000
Fixed payments [Member] | Aggregate 2016 Step Up Transactions [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred					542
Noncontrolling Interest Equity [Domain] | Aggregate 2016 Step Up Transactions [Member]
Business Acquisition [Line Items]
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests					19,194
Common Class A [Member] | Common Stock [Member]
Business Acquisition [Line Items]
Business Acquisition, Pro Forma Net Income (Loss)
Common Class A [Member] | Common Stock [Member] | Forsman & Bodenfors AB [Domain]
Business Acquisition [Line Items]
Stock Issued During Period, Shares, Acquisitions		1,900,000
Stock Issued During Period, Value, Acquisitions	$ 21,371	$ 34,219,000			$ 34,219,000	$ 0