Prepaid Expenses and Other Current Assets and Accrued and Other Current Liabilities Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Other Current Assets And Other Current Liabilities [Abstract]
Prepaid expenses	$ 3,624	$ 1,794
Securities litigation insurance receivable	242	16,627
Other current assets	594	920
Prepaid expenses and other current assets	$ 4,460	$ 19,341