Geographical Information (Long-Lived Assets, Net By Geographic Region) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Long-lived assets, net	$ 11,591	$ 31,087
United States [Member]
Segment Reporting Information [Line Items]
Long-lived assets, net	2,741	11,276
United Kingdom [Member]
Segment Reporting Information [Line Items]
Long-lived assets, net	7,098	17,968
Other [Member]
Segment Reporting Information [Line Items]
Long-lived assets, net	$ 1,752	$ 1,843