Share capital - Warrants (Details)	12 Months Ended
	Dec. 31, 2019 USD ($) $ / shares shares
Class of Warrant or Right [Line Items]
Maximum percent of warrants reserved for issuance	4.00%
Maximum value of warrants reserved for issuance	$ 1,000,000,000
Exercise price (in dollars per share) | $ / shares	$ 10.00
Authorized and issued (in shares) | shares	3,494,979
Aggregated fair value of warrants	$ 13,055,000
Term of warrants	10 years
Founders
Class of Warrant or Right [Line Items]
Maximum percent of warrants reserved for issuance	3.50%
Exercise price (in dollars per share) | $ / shares	$ 10.00
Authorized and issued (in shares) | shares	2,913,684
Aggregated fair value of warrants	$ 10,884,000
Advisor
Class of Warrant or Right [Line Items]
Maximum percent of warrants reserved for issuance	0.50%
Exercise price (in dollars per share) | $ / shares	$ 10.00
Authorized and issued (in shares) | shares	581,295
Aggregated fair value of warrants	$ 2,171,000