Deferred Acquisition Consideration (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance of contingent payments	$ 82,598	$ 119,086	$ 119,086
Payments	(275)		(54,947)
Redemption value adjustments	(6,834)	4,947	3,512
Additions	0		14,943
Foreign translation adjustment	59		4
Ending balance of contingent payments	75,548		82,598
Deferred acquisition consideration	76,383		83,695
Stock-based compensation	809	2,361
Fixed payments
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Deferred acquisition consideration	835		$ 1,097
Contingent Payment
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Income (loss) attributable to fair value adjustments	$ (7,643)	$ 2,586