Income Taxes - Reconciliation of Tax Rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Statutory tax rate	12.49945%	12.50%	12.50%
Differences in international tax rates	8.00%	22.20%	(31.90%)
Nondeductible changes in fair value of contingent consideration	4.00%	(11.60%)	(165.00%)
Income tax deferred charge	0.00%	0.00%	(9.70%)
Change in valuation allowances	(5.30%)	(0.70%)	11.80%
Nondeductible stock-based compensation	(1.30%)	(0.40%)	(14.80%)
Cross border merger	0.00%	0.30%	(100.60%)
Unrealized tax benefits	(1.30%)	1.40%	(15.20%)
State and local taxes (net of federal)	(0.30%)	0.30%	(9.60%)
Change in U.S. tax law	(0.20%)	3.80%	0.00%
Nondeductible interest expense	(1.10%)	0.00%	0.00%
Other	0.70%	(1.50%)	(2.30%)
Effective income tax rate	15.70%	26.30%	(324.80%)
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Income tax provision (benefit) - at statutory tax rate	$ (14,149)	$ 11,582	$ (1,215)
International tax rates differential	(9,039)	20,557	3,097
Nondeductible changes in fair value of contingent consideration	(4,559)	(10,779)	16,036
Income tax deferred charge	0	0	938
Change in valuation allowances	5,998	(610)	(1,143)
Nondeductible stock-based compensation	1,499	(375)	1,436
Cross-border merger	0	265	9,773
Unrecognized tax benefits	1,440	1,296	1,475
State and local taxes (net of federal)	299	252	934
Change in U.S. tax law	274	3,513	0
Nondeductible interest expense	1,269	0	0
Other	(925)	(1,312)	227
Income tax (benefit) provision	$ (17,893)	$ 24,389	$ 31,558