Description of Business and Summary of Significant Accounting Policies - Schedule of Computation of Diluted Net Loss per Share of Common Stock Attributable to Common Stockholders (Parenthetical) (Details) - USD ($)	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Aug. 31, 2018
Long Term Debt With Related Parties [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Aggregate principal amount	$ 43,664,000	$ 62,478,000
Secured Convertible Promissory Notes [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Secured convertible promissory notes	4,000,000.0		$ 4,000,000.0	$ 4,000,000.0
Secured Convertible Promissory Notes [Member] | Long Term Debt With Related Parties [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Aggregate principal amount		3,280,000
Four Promissory Notes Issued February 1, 2017 to Former EAF [Member] | Long Term Debt With Related Parties [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Aggregate principal amount	$ 9,500,000	$ 9,500,000	$ 9,500,000