Convertible Preferred Stock and Stockholders' Deficit - Summary of Outstanding Convertible Preferred Stock Warrants (Details) shares in Thousands	6 Months Ended
	Jun. 30, 2018 $ / shares shares
Class Of Warrant Or Right [Line Items]
Warrants Outstanding	3,046
Series E Convertible Preferred Stock Warrants
Class Of Warrant Or Right [Line Items]
Warrants Outstanding	402
Exercise Price | $ / shares	$ 0.6746
Expiration Date	2022-12
Series F Convertible Preferred Stock Warrants
Class Of Warrant Or Right [Line Items]
Warrants Outstanding	878
Exercise Price | $ / shares	$ 0.3356
Expiration Date	2021-02
Series F Convertible Preferred Stock Warrants
Class Of Warrant Or Right [Line Items]
Warrants Outstanding	589
Exercise Price | $ / shares	$ 0.3356
Expiration Date	2023-08
Series F Convertible Preferred Stock Warrants
Class Of Warrant Or Right [Line Items]
Warrants Outstanding	589
Exercise Price | $ / shares	$ 0.3356
Expiration Date	2024-03
Series F Convertible Preferred Stock Warrants
Class Of Warrant Or Right [Line Items]
Warrants Outstanding	588
Exercise Price | $ / shares	$ 0.3356
Expiration Date	2024-12