Warrants for Convertible Preferred Stock - Summary of Activity for Convertible Preferred Stock Warrants Outstanding (Details) shares in Thousands	9 Months Ended
	Sep. 30, 2020 $ / shares shares
Series E Convertible Preferred Stock Warrants
Class Of Warrant Or Right [Line Items]
Outstanding ‑ December 31, 2019, warrants | shares	925
Forfeited/canceled, warrants | shares	(925)
Weighted average exercise price, Outstanding ‑ December 31, 2019 | $ / shares	$ 5.00
Weighted average exercise price, Forfeited/canceled | $ / shares	$ (5.00)
Series G Convertible Preferred Stock Warrants
Class Of Warrant Or Right [Line Items]
Outstanding ‑ December 31, 2019, warrants | shares	613
Outstanding ‑ September 30, 2020, warrants | shares	613
Weighted average remaining contractual life at September 30, 2020	7 years 6 months
Weighted average exercise price, Outstanding ‑ December 31, 2019 | $ / shares	$ 0.75
Weighted average exercise price,Outstanding ‑ September 30, 2020 | $ / shares	$ 0.75