Balance Sheet Components - Schedule of Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Prepaid Expense And Other Assets Current [Abstract]
Prepaid expenses	$ 120	$ 129
Prepaid insurance	1,653	858
Prepaid research and development expenses	2,778	4,517
Other current assets	629	688
Total prepaid expenses and other current assets	$ 5,180	$ 6,192