Income taxes - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2020	Dec. 31, 2018	Dec. 31, 2017
Operating Loss Carryforwards [Line Items]
Federal net operating loss carryforwards		$ 400
State net operating loss carryforwards		$ 300
Net operating loss carryforwards period		20 years
Unrecognized tax benefits that would impact effective tax rate	$ 400	$ 500	$ 400
Unrecognized tax benefits expected to reverse in next twelve months		100
Accrued gross interest and penalties	100	100	100
Recognized net interest expense	$ 0	$ 0	$ (40)	$ 17
Minimum
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards period		5 years
Maximum
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards period		20 years