Summary of significant accounting policies - Schedule of Useful Lives of Property and Equipment (Details)	12 Months Ended
	Mar. 31, 2020
Equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives of property and equipment	1 year
Equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives of property and equipment	8 years
Motor vehicles | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives of property and equipment	3 years
Motor vehicles | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives of property and equipment	7 years
Furniture, fixtures and equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives of property and equipment	1 year
Furniture, fixtures and equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives of property and equipment	10 years
Computer equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives of property and equipment	1 year
Computer equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives of property and equipment	7 years
In-vehicle devices installed | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives of property and equipment	1 year
In-vehicle devices installed | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives of property and equipment	6 years 6 months