Other Assets and Liabilities - Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Prepaid Expenses and Other Current Assets:
Valued-added tax recoverable	$ 257	$ 1,051
Prepaid and other expenses	1,933	2,116
Guarantee from Armistice	456	454
Income tax receivable	536	536
Research and development tax credit receivable	1,835	2,107
Other	155	107
Total	$ 3,337	$ 4,264