Entity Wide Disclosures - Summary of Property and Equipment, Net by Geographic Region (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property and equipment, net:
Property and equipment, net	$ 48,739	$ 43,805
U.S.
Property and equipment, net:
Property and equipment, net	37,535	34,817
Europe [Member]
Property and equipment, net:
Property and equipment, net	9,266	7,436
Other
Property and equipment, net:
Property and equipment, net	$ 1,938	$ 1,552