Acquisitions and Dispositions (Details Textual) - USD ($)						3 Months Ended		12 Months Ended
	Mar. 08, 2019	Sep. 07, 2018	Jul. 01, 2018	Apr. 02, 2018	Jan. 01, 2018	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Business Acquisition [Line Items]
Goodwill						$ 742,775,000		$ 740,955,000
Deferred acquisition consideration						76,383,000		83,695,000
Business acquisitions and step-up transactions, net of tax							$ (1,166,000)
Granted						0		0
Aggregate 2018 Step-up Transaction [Member] [Member]
Business Acquisition [Line Items]
Closing cash payment				$ 3,279,000
Business Acquisition Deferred Acquisition Consideration								4,305
Instrument LLC [Member]
Business Acquisition [Line Items]
Remaining ownership interest acquired (percent)				51.00%
Business Combination, Consideration Transferred, Other				$ 10,304,000
Finite-lived Intangible Assets Acquired				23,130,000
Goodwill				32,776
Aggregate purchase price				35,591,000
Closing cash payment				28,561,000
Granted				$ 27,357,000
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life				6 years
Allison & Partners LLC
Business Acquisition [Line Items]
Remaining ownership interest acquired (percent)					24.50%
Aggregate purchase price					$ 10,023,000
Closing cash payment					300,000
Deferred acquisition consideration					9,723,000
Business Combination, Consideration Transferred, Including Equity Interest in Acquiree Held Prior to Combination					20,096
Business acquisitions and step-up transactions, net of tax					(8,857,000)
Granted					$ 1,166,000
OneChocolate [Domain]
Business Acquisition [Line Items]
Remaining ownership interest acquired (percent)		100.00%
Aggregate purchase price		$ 3,231,000
Business Acquisition Working Capital Payments								966
Doner [Domain]
Business Acquisition [Line Items]
Remaining ownership interest acquired (percent)			14.87%
Business Combination, Consideration Transferred, Including Equity Interest in Acquiree Held Prior to Combination								$ 16,361
Source [Domain]
Business Acquisition [Line Items]
Remaining ownership interest acquired (percent)			3.00%
Doner and Source [Domain]
Business Acquisition [Line Items]
Aggregate purchase price			$ 7,618,000
Business acquisitions and step-up transactions, net of tax			(11,946,000)
Reduction in noncontrolling interests			$ 933,000
Common Class A [Member] | Common Stock [Member] | Instrument LLC [Member]
Business Acquisition [Line Items]
Stock Issued During Period, Shares, Acquisitions				1,011,561
Stock Issued During Period, Value, Acquisitions				$ 7,030,000
Kingsdale Partners LP [Member]
Business Acquisition [Line Items]
Proceeds from Divestiture of Businesses						$ 50,000,000
Loss on disposition of business	$ (3,000,000)