Property, plant and equipment - Schedule of Owned Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Mar. 31, 2022
Property, Plant and Equipment [Line Items]
Owned assets, gross	$ 75,274	$ 74,531
Less: accumulated depreciation and impairments	(44,905)	(46,597)
Owned assets, net	30,369	27,934
Plant and Equipment
Property, Plant and Equipment [Line Items]
Owned assets, gross	715	791
Motor Vehicles
Property, Plant and Equipment [Line Items]
Owned assets, gross	1,814	1,938
Furniture, fixtures and equipment
Property, Plant and Equipment [Line Items]
Owned assets, gross	1,357	1,553
Computer and radio equipment
Property, Plant and Equipment [Line Items]
Owned assets, gross	3,745	4,036
In-vehicle devices
Property, Plant and Equipment [Line Items]
Owned assets, gross	67,532	65,881
Assets in progress
Property, Plant and Equipment [Line Items]
Owned assets, gross	$ 111	$ 332