Supplemental Balance Sheet Information - Accrued Expense and Other Current Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Supplemental Balance Sheet Information [Abstract]
Accrued payroll-related expenses	$ 706	$ 920
Accrued legal expenses	362	254
Operating lease liability	196	292
Common stock warrant liability	257	0
Accrued clinical, contract research and manufacturing costs	303	515
Accrued other expenses	123	454
Accrued expenses and other current liabilities	$ 1,947	$ 2,435