Income taxes - Textual (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Operating Loss Carryforwards [Line Items]
Income tax benefits	$ 24
Net operating loss carry forwards	11,380	$ 2,899
Deferred Tax Assets, Operating Loss Carryforwards, Not Subject to Expiration	48,757
Deferred Tax Assets, Tax Credit Carryforwards, Research	969	231
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount	(8,712)	$ (5,438)
Accrued interest or penalties related to uncertain tax positions	0
Gross unrecognized tax benefit	237
Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carry forwards	51,094
Deferred Tax Assets, Tax Credit Carryforwards, Research	1,058
NOL carryforwards that expire	2,200
State
Operating Loss Carryforwards [Line Items]
Net operating loss carry forwards	10,222
Deferred Tax Assets, Tax Credit Carryforwards, Research	187
NOL carryforwards that expire	3,700
General and Administrative Expense
Operating Loss Carryforwards [Line Items]
Income tax benefits	$ 24