Entity Wide Disclosures - Summary of Property and Equipment, Net by Geographic Region (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Property and equipment, net:
Property and equipment, net	$ 52,255	$ 48,739
U.S.
Property and equipment, net:
Property and equipment, net	38,609	37,535
Europe, Belgium
Property and equipment, net:
Property and equipment, net	6,014	4,132
Europe, Other
Property and equipment, net:
Property and equipment, net	5,500	5,134
Europe
Property and equipment, net:
Property and equipment, net	11,514	9,266
Other
Property and equipment, net:
Property and equipment, net	$ 2,132	$ 1,938