Geographical Information (Long-Lived Assets, Net By Geographic Region) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Long-lived assets, net	$ 29,873	$ 31,087
United States [Member]
Segment Reporting Information [Line Items]
Long-lived assets, net	10,745	11,276
United Kingdom [Member]
Segment Reporting Information [Line Items]
Long-lived assets, net	17,252	17,968
Other [Member]
Segment Reporting Information [Line Items]
Long-lived assets, net	$ 1,876	$ 1,843