Income Taxes - Reconciliation of Tax Rate (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Statutory tax rate	12.50%	12.50%
International tax rates differential	8.90%	17.00%
Change in valuation allowance	(4.70%)	2.00%
Nondeductible change in fair value of contingent consideration	(3.80%)	(7.20%)
Nondeductible stock-based compensation	(1.10%)	(0.20%)
Unrecognized tax benefits	(1.50%)	0.80%
State and local income taxes, net of federal	0.10%	0.10%
Change in U.S. tax law	0.00%	0.00%
Other	5.60%	(0.20%)
Effective income tax rate	16.00%	24.80%
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Income tax (benefit) provision - at statutory tax rate	$ (1,820)	$ 4,306
International tax rates differential	(1,298)	5,860
Change in valuation allowance	690	684
Nondeductible change in fair value of contingent consideration	551	(2,476)
Nondeductible stock-based compensation	160	(55)
Unrecognized tax benefits	220	259
State and local income taxes, net of federal	(19)	34
Change in U.S. tax law	0	0
Other	(811)	(73)
Income tax (benefit) provision - at effective income tax rate	$ (2,327)	$ 8,539