Fair value measurements - Assets and liabilities measured at fair value (Details)	9 Months Ended
	Sep. 30, 2020 USD ($)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Transfers, Net [Abstract]
Transfer into Level 3	$ 0
Transfer out of Level 3	0
Recurring
Liabilities:
Warrant liability	7,071,000
Total liabilities measured and recorded at fair value	7,071,000
Level 3 | Recurring
Liabilities:
Warrant liability	7,071,000
Total liabilities measured and recorded at fair value	$ 7,071,000