Property, plant and equipment - Schedule of Owned Property and Equipment (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Mar. 31, 2021
Property, Plant and Equipment [Line Items]
Owned equipment, gross	$ 74,531	$ 60,325
Less: accumulated depreciation and impairments	(46,597)	(42,955)
Owned assets, net	27,934	17,370
Plant and equipment
Property, Plant and Equipment [Line Items]
Owned equipment, gross	791	719
Motor vehicles
Property, Plant and Equipment [Line Items]
Owned equipment, gross	1,938	993
Furniture, fixtures and equipment
Property, Plant and Equipment [Line Items]
Owned equipment, gross	1,553	1,519
Computer and radio equipment
Property, Plant and Equipment [Line Items]
Owned equipment, gross	4,036	3,639
In-vehicle devices
Property, Plant and Equipment [Line Items]
Owned equipment, gross	65,881	53,448
Assets in progress
Property, Plant and Equipment [Line Items]
Owned equipment, gross	$ 332	$ 7