Fair value measurements - Additional Information (Detail) - Warrants	6 Months Ended
	Jun. 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]
Measurment input	0.4262
Risk-free interest rate
Foreign Currency Fair Value Hedge Derivative [Line Items]
Measurment input	0.0016
Minimum | Expected volatility
Foreign Currency Fair Value Hedge Derivative [Line Items]
Measurment input	0.271
Maximum | Expected volatility
Foreign Currency Fair Value Hedge Derivative [Line Items]
Measurment input	0.598