Income Taxes - Reconciliation of Tax Rate (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Statutory tax rate	12.50%	12.50%	12.50%	12.50%
International tax rates differential	7.00%	24.90%	6.90%	20.50%
Change in valuation allowance	(18.30%)	(1.60%)	(14.90%)	0.50%
Change in fair value of nondeductible contingent consideration	8.70%	(12.80%)	9.90%	(10.90%)
Nondeductible stock-based compensation	(3.50%)	(0.40%)	(2.60%)	(0.30%)
Unrecognized tax benefits	(3.50%)	0.90%	(3.10%)	0.80%
State and local income taxes, net of federal	0.10%	0.00%	0.20%	0.10%
Change in U.S. tax law	0.00%	0.00%	0.00%	0.00%
Other	1.20%	(2.10%)	0.80%	(0.90%)
Effective income tax rate	4.20%	21.40%	9.70%	22.30%
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Income tax (benefit) provision - at statutory tax rate	$ (2,058)	$ 3,449	$ (4,351)	$ 12,294
International tax rates differential	(1,153)	6,861	(2,394)	20,120
Change in valuation allowance	3,007	(438)	5,188	476
Change in fair value of nondeductible contingent consideration	(1,431)	(3,521)	(3,436)	(10,751)
Nondeductible stock-based compensation	578	(116)	914	(265)
Unrecognized tax benefits	578	262	1,086	771
State and local income taxes, net of federal	(13)	(6)	(70)	69
Change in U.S. tax law	0	0	0	0
Other	(199)	(570)	(297)	(884)
Income tax (benefit) provision - at effective income tax rate	$ (691)	$ 5,921	$ (3,360)	$ 21,830