Acquisitions (Details Textual) - USD ($)			3 Months Ended		6 Months Ended	9 Months Ended		12 Months Ended
	Apr. 05, 2017	Jul. 01, 2016	Sep. 30, 2017	Sep. 30, 2016	Jun. 30, 2017	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016	Apr. 01, 2016
Business Acquisition [Line Items]
Adjustments to deferred acquisition consideration included in share-based compensation			$ 4,064	$ 2,259		$ 9,792	$ 7,184
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests			(337,000)	(520,000)		(9,650,000)
Noncontrolling Interest, Increase from Business Combination						2,315,000	22,498,000
Stock-based compensation			6,380,000	5,228,000		16,870,000	15,443,000
Goodwill, Written off Related to Sale of Business Unit						17,593,000	764,000
Business Acquisition, Pro Forma Net Income (Loss)			18,493,000	(32,140,000)		19,180,000	(54,937,000)
Redeemable noncontrolling interests			$ 60,092,000			$ 60,092,000		$ 60,180,000
Noncontrolling Interest, Ownership Percentage by Parent			100.00%			100.00%
Net Income Loss Including Transfer from Non Controlling Interests			$ 18,156,000	(32,660,000)		$ 21,495,000	(32,439,000)
Forsman & Bodenfors AB [Domain]
Business Acquisition [Line Items]
Business Acquisition, Pro Forma Revenue					$ 43,535
Business Acquisition, Pro Forma Net Income (Loss)					4,460
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, Percentage of Voting Interests Acquired		100.00%
Business Combination, Consideration Transferred		$ 49,837
Business Combination, Contingent Consideration, Liability		$ 15,618			$ 3,055
Luntz Global Partners L L C
Business Acquisition [Line Items]
Business Acquisition, Percentage of Voting Interests Acquired									40.00%
Aggregate 2017 Step Up Transactions [Domain]
Business Acquisition [Line Items]
Business Acquisition, Cost of Acquired Entity, Cash Paid						3,858
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests						(11,965)
Noncontrolling Interest, Period Increase (Decrease)						397
Noncontrolling Interest, Increase from Business Combination						2,316
Stock-based compensation						996
Business Combination, Acquisition of Less than 100 Percent, Redeemable Noncontrolling Interest, Fair Value						816
Business Combination, Contingent Consideration, Liability			7,208			7,208
Aggregate 2016 Step Up Transactions [Member]
Business Acquisition [Line Items]
Business Acquisition, Cost of Acquired Entity, Cash Paid								1,581
Business Combination, Acquisition of Less than 100 Percent, Redeemable Noncontrolling Interest, Fair Value								1,005
Business Combinations, Assets Relinquished by Acquirer								428
Business Combinations, Liabilities Relinquished Previously due to Acquiree								94
Noncontrolling Interest [Member]
Business Acquisition [Line Items]
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests						(11,965,000)
Business Acquisition, Pro Forma Net Income (Loss)						0
Additional Paid-in Capital [Member]
Business Acquisition [Line Items]
Noncontrolling Interest, Increase from Business Combination						2,315,000
Additional Paid-in Capital [Member] | Aggregate 2016 Step Up Transactions [Member]
Business Acquisition [Line Items]
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests								(22,775)
Contingent payment [Domain]
Business Acquisition [Line Items]
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability			$ (2,462,000)	$ 11,152,000		$ 12,152,000	$ 17,180,000
Contingent payment [Domain] | Aggregate 2016 Step Up Transactions [Member]
Business Acquisition [Line Items]
Deferred Stock-based Compensation, Discounted								2,393
Business Combination, Consideration Transferred								4,052,000
Fixed payments [Member] | Aggregate 2016 Step Up Transactions [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred								467
Noncontrolling Interest Equity [Domain] | Aggregate 2016 Step Up Transactions [Member]
Business Acquisition [Line Items]
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests								$ (19,354)
Common Class A [Member] | Common Stock [Member] | Forsman & Bodenfors AB [Domain]
Business Acquisition [Line Items]
Stock Issued During Period, Shares, Acquisitions	2,450,000	1,900,000
Stock Issued During Period, Value, Acquisitions	$ 20,800	$ 34,219,000