Income Taxes (Summary of Valuation Allowance) (Details) - Deferred Tax Valuation Allowance - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance as of January 1	$ 1,362	$ 766	$ 400
Cost charged to the tax provision	1,505	983	286
Currency translation	(820)	(338)	(78)
Currency translation	195	(49)	0
Balance as of December 31	$ 2,242	$ 1,362	$ 766