Other Assets and Liabilities - Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Prepaid Expenses and Other Current Assets:
Valued-added tax recoverable	$ 671	$ 1,378
Prepaid and other expenses	2,594	2,145
Guarantee from Armistice	551	534
Income tax receivable	997	921
Research and development tax credit receivable	270	283
Short-term deposit	0	3,350
Other	82	225
Total	$ 5,165	$ 8,836