Other Assets and Liabilities - Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Other Liabilities Disclosure [Abstract]
Valued-added tax recoverable	$ 1,378	$ 1,206
Prepaid and other expenses	2,145	7,106
Guarantee from Armistice (see Note 16)	534	0
Income tax receivable	921	518
Research and development tax credit receivable	283	0
Short-term deposit	3,350	0
Other	225	128
Total	$ 8,836	$ 8,958