Acquisitions (Details Textual) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015	Apr. 01, 2016	Oct. 01, 2015	May 01, 2015
Business Acquisition [Line Items]
Adjustments to deferred acquisition consideration included in share-based compensation	$ 2,020	$ 2,245	$ 4,925	$ 4,914
Redeemable Noncontrolling Interest, Equity, Fair Value	$ 65,367,000		$ 65,367,000		$ 69,471,000
Noncontrolling Interest, Ownership Percentage by Parent	100.00%		100.00%
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			$ 654
Business Combinations, Assets Relinquished by Acquirer			428
Business Combinations, Liabilities Relinquished Previously due to Acquiree			33
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
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] | Aggregate 2016 Step Up Transactions [Member]
Business Acquisition [Line Items]
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests			23,018
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	$ (299,000)	$ (12,741,000)	6,028,000	$ (10,493,000)
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] | Aggregate 2016 Step Up Transactions [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred			841
Noncontrolling Interest Equity [Domain] | Aggregate 2016 Step Up Transactions [Member]
Business Acquisition [Line Items]
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests			$ 19,174