Long-term debt - Long-Term Debt (Parenthetical) (Detail)	12 Months Ended					0 Months Ended
	Dec. 31, 2013 USD ($)	Dec. 31, 2013 CAD	Dec. 31, 2012 USD ($)	Dec. 31, 2011 USD ($)	Dec. 31, 2012 CAD	Nov. 01, 2012 Canadian Real Estate Facilities [Member]	Nov. 30, 2011 Canadian Real Estate Facilities [Member]	Dec. 31, 2013 Canadian Real Estate Facilities [Member] CAD Terminal	Dec. 31, 2012 Canadian Real Estate Facilities [Member] CAD	Dec. 31, 2013 Canadian Real Estate Facilities [Member] Minimum [Member]	Dec. 31, 2012 Canadian Real Estate Facilities [Member] Minimum [Member]	Dec. 31, 2013 Canadian Real Estate Facilities [Member] Maximum [Member]	Dec. 31, 2012 Canadian Real Estate Facilities [Member] Maximum [Member]
Debt Instrument [Line Items]
Number of transportation terminals								5
Canadian real estate outstanding amount								49,100,000	50,200,000
Interest rate										4.30%	4.30%	4.75%	4.75%
Maturity date						Nov. 30, 2018	Nov. 30, 2018
Capital lease Additions, consolidated	4,988,000	5,300,000	5,745,000	1,317,000
Capital lease remaining	$ 5,953,000	6,300,000	$ 1,307,000		1,300,000