Significant accounting policies - Summary of Estimated Useful Lives of Property and Equipment (Detail)	12 Months Ended
	Dec. 31, 2013
Buildings [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	30 years
Leasehold interests and improvements [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	Over term of lease
Vehicles - Trailers and containers [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	12 years
Vehicles - Trucks [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	8 years
Minimum [Member] | Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	4 years
Maximum [Member] | Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	10 years