Fair value measurements - Additional Information (Detail) - Warrants	9 Months Ended
	Sep. 30, 2020
Warrant life
Foreign Currency Fair Value Hedge Derivative [Line Items]
Expected option life	2 years
Expected volatility
Foreign Currency Fair Value Hedge Derivative [Line Items]
Measurement input	0.4361
Risk-free interest rate
Foreign Currency Fair Value Hedge Derivative [Line Items]
Measurement input	0.0013
Minimum | Expected volatility
Foreign Currency Fair Value Hedge Derivative [Line Items]
Measurement input	0.2875
Maximum | Expected volatility
Foreign Currency Fair Value Hedge Derivative [Line Items]
Measurement input	0.6186