Deferred Acquisition Considerations (Details) - USD ($)	3 Months Ended		12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance of contingent payments			$ 119,086,000	$ 224,754,000
Payments			(54,947,000)	(110,234,000)
Additions - acquisition and step-up transactions			14,943,000	0
Redemption value adjustments			3,512,000	3,273,000
Foreign translation adjustment			4,000	1,293,000
Ending balance of contingent payments	$ 82,598,000	$ 119,086,000	82,598,000	119,086,000	$ 224,754,000
Fixed payments	83,695,000	122,426,000	83,695,000	122,426,000
Income attributable to fair value adjustments			(374,000)	(4,819,000)	8,227,000
Stock-based compensation expense			7,191,000	9,294,000
Common Class A
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Redemption value adjustments				3,353,939
Contingent Payment [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Income attributable to fair value adjustments	8,979,000	18,173,000	(3,679,000)	(6,021,000)
Fixed payments [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Payments			6,000
Fixed payments	$ 1,097,000	$ 3,340,000	1,097,000	3,340,000
Common Stock
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Redemption value adjustments			$ 0
Common Stock | Common Class A
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Redemption value adjustments				$ 28,727,000	$ 10,458,000