Segment Information (Schedule of Fixed Assets by Geographic Location) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Revenues from External Customers and Long-Lived Assets [Line Items]
Property and equipment, net	$ 183,514	$ 166,636
North America [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Property and equipment, net	136,203	104,939
Europe [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Property and equipment, net	28,261	39,976
Other Geographic Locations [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Property and equipment, net	$ 19,050	$ 21,721