Fair Value Measurements - Weighted-average assumptions (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
Expected term
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt instrument measurement input	6.73	6.98
Expected volatility
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