Supplemental Balance Sheet Information - Accrued Expense and Other Current Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Supplemental Balance Sheet Information [Abstract]
Accrued payroll-related expenses	$ 386	$ 920
Accrued legal expenses	318	254
Operating lease liability	275	292
Accrued clinical, contract research and manufacturing costs	152	515
Accrued other expenses	137	454
Accrued expenses and other current liabilities	$ 1,268	$ 2,435