Summary of significant accounting policies - Property, Plant and Equipment (Detail) (Details)	12 Months Ended
	Dec. 30, 2017
Buildings | Minimum
Property, Plant and Equipment [Line Items]
Useful life of property plant and equipment	20 years
Buildings | Maximum
Property, Plant and Equipment [Line Items]
Useful life of property plant and equipment	35 years
Leasehold improvements | Minimum
Property, Plant and Equipment [Line Items]
Useful life of property plant and equipment	5 years
Leasehold improvements | Maximum
Property, Plant and Equipment [Line Items]
Useful life of property plant and equipment	20 years
Equipment | Minimum
Property, Plant and Equipment [Line Items]
Useful life of property plant and equipment	3 years
Equipment | Maximum
Property, Plant and Equipment [Line Items]
Useful life of property plant and equipment	10 years
Software Development | Minimum
Property, Plant and Equipment [Line Items]
Useful life of property plant and equipment	3 years
Software Development | Maximum
Property, Plant and Equipment [Line Items]
Useful life of property plant and equipment	7 years