Fair Value Measurements - Weighted-average assumptions (Details)	Dec. 31, 2020 $ / shares	Dec. 31, 2019 $ / shares
Risk-free interest rate
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input	0.0050	0.0179
Expected term
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input	0.0598	0.0698
Expected volatility
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input	0.80	0.80
Exercise price
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input	1.52	1.52