Fair Value of Financial Assets (Schedule of Financial Assets Measured at Fair Value) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	$ 68,509	$ 30,731
Other asset – advance payment to supplier	2,033	1,472
Total	70,542	32,203
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	68,509	30,731
Total	68,509	30,731
Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Other asset – advance payment to supplier	2,033	1,472
Total	$ 2,033	$ 1,472