Fair Value Measurements - Future Tranche Rights (Details)	Mar. 31, 2020 $ / shares USD ($)	Dec. 31, 2019 $ / shares USD ($)
Risk-free interest rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt instrument measurement input	0.53	1.79
Risk-free interest rate | Warrants
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt instrument measurement input	0.53	1.79
Risk-free interest rate | Preferred stock | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt instrument measurement input	0.59	1.84
Risk-free interest rate | Preferred stock | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt instrument measurement input	0.65	1.88
Expected term
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt instrument measurement input	6.73	6.98
Expected term | Warrants | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt instrument measurement input	7.91	8.16
Expected term | Warrants | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt instrument measurement input	8.91	9.16
Expected term | Preferred stock | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt instrument measurement input	0.91	1.16
Expected term | Preferred stock | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt instrument measurement input	1.91	2.16
Expected volatility
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt instrument measurement input	80	80
Expected volatility | Future tranche right liability
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt instrument measurement input	80	80
Exercise price
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt instrument measurement input | $ / shares	1.52	1.52
Exercise price | Future tranche right liability | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt instrument measurement input	1.52	1.52
Exercise price | Future tranche right liability | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt instrument measurement input	1.82	1.82