Balance Sheets 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]
Advance to suppliers		$ 3,338
Prepaid expenses	$ 1,921	1,279
Other current assets	1,054	984
Total prepaid and other current assets	$ 2,975	$ 5,601