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Fair value of financial assets and liabilities - Weighted Average of the Unobservable Inputs Used to Fair Value (Details) - Level 3	3 Months Ended		9 Months Ended
	Sep. 30, 2021 Y $ / shares	Sep. 30, 2020 Y $ / shares	Sep. 30, 2021 Y $ / shares	Sep. 30, 2020 Y $ / shares
Remaining contractual term (in years)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Preferred stock warrant liability, measurement input | Y	6.6	7.4	6.8	7.7
Risk-free interest rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Preferred stock warrant liability, measurement input	0.010	0.006	0.012	0.006
Expected volatility
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Preferred stock warrant liability, measurement input	0.422	0.403	0.420	0.393
Series A1 Redeemable Convertible Preferred Stock
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value of preferred stock warrant liability	$ 4.00	$ 0.39	$ 3.01	$ 0.45
Series B1 Redeemable Convertible Preferred Stock
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value of preferred stock warrant liability	4.00	1.17	3.26	1.13
Series C1 Redeemable Convertible Preferred Stock
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value of preferred stock warrant liability	$ 4.00	$ 1.15	$ 3.30	$ 1.15

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- Definition

Fair value per share of preferred stock warrants.

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- Definition

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- Definition

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