Common Stock Warrant Liabilities (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) shares	May 17, 2019 USD ($)	Dec. 31, 2018 USD ($)
Class of Warrant or Right [Line Items]
Convertible warrant liabilities	$ 0	$ 5,665	$ 3,261
Common Stock Warrants, Series B
Class of Warrant or Right [Line Items]
Convertible warrant liabilities		1,818	857
Common Stock Warrants, Series C
Class of Warrant or Right [Line Items]
Convertible warrant liabilities		792	407
Common Stock Warrants, Series D
Class of Warrant or Right [Line Items]
Convertible warrant liabilities		668	358
Common Stock Warrants, Series F
Class of Warrant or Right [Line Items]
Convertible warrant liabilities		$ 2,387	$ 1,639
Expected remaining term (in years) | Common Stock Warrants, Series B
Class of Warrant or Right [Line Items]
Expected remaining term		4 years 5 months 15 days	4 years 10 months 2 days
Expected remaining term (in years) | Common Stock Warrants, Series C
Class of Warrant or Right [Line Items]
Expected remaining term		5 years 5 months 19 days	5 years 10 months 2 days
Expected remaining term (in years) | Common Stock Warrants, Series D
Class of Warrant or Right [Line Items]
Expected remaining term		7 years 2 months 15 days	7 years 7 months 2 days
Expected remaining term (in years) | Common Stock Warrants, Series F
Class of Warrant or Right [Line Items]
Expected remaining term		9 years 7 months 13 days	10 years
Risk-free interest rate | Common Stock Warrants, Series B
Class of Warrant or Right [Line Items]
Measurement input		0.0217	0.0262
Risk-free interest rate | Common Stock Warrants, Series C
Class of Warrant or Right [Line Items]
Measurement input		0.0220	0.0262
Risk-free interest rate | Common Stock Warrants, Series D
Class of Warrant or Right [Line Items]
Measurement input		0.0227	0.0262
Risk-free interest rate | Common Stock Warrants, Series F
Class of Warrant or Right [Line Items]
Measurement input		0.0237	0.0280
Expected volatility | Common Stock Warrants, Series B
Class of Warrant or Right [Line Items]
Measurement input		0.390	0.500
Expected volatility | Common Stock Warrants, Series C
Class of Warrant or Right [Line Items]
Measurement input		0.393	0.500
Expected volatility | Common Stock Warrants, Series D
Class of Warrant or Right [Line Items]
Measurement input		0.402	0.500
Expected volatility | Common Stock Warrants, Series F
Class of Warrant or Right [Line Items]
Measurement input		0.424	0.500
Dividend yield | Common Stock Warrants, Series B
Class of Warrant or Right [Line Items]
Measurement input		0	0
Dividend yield | Common Stock Warrants, Series C
Class of Warrant or Right [Line Items]
Measurement input		0	0
Dividend yield | Common Stock Warrants, Series D
Class of Warrant or Right [Line Items]
Measurement input		0	0
Dividend yield | Common Stock Warrants, Series F
Class of Warrant or Right [Line Items]
Measurement input		0	0
Common Stock | Common Class B
Class of Warrant or Right [Line Items]
Exercise of common stock warrants (in shares) | shares	224,102
Common Stock | Common Stock Warrants, Series B | Common Class B
Class of Warrant or Right [Line Items]
Exercise of common stock warrants (in shares) | shares	224,102