Long-term debt - Additional Information (Detail) In Millions, unless otherwise specified	0 Months Ended	12 Months Ended				0 Months Ended			12 Months Ended
	Oct. 07, 2013 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2011 USD ($)	Mar. 04, 2013 USD ($)	Nov. 30, 2011 USD ($)	Nov. 01, 2012 Canadian Real Estate Facilities [Member] CAD	Nov. 30, 2011 Canadian Real Estate Facilities [Member] CAD	Nov. 30, 2011 Revolving credit facility [Member] USD ($)	Dec. 31, 2013 U.S. LTL [Member] USD ($)	Dec. 31, 2013 SCO [Member] USD ($)
Line of Credit Facility [Line Items]
Amended maximum borrowing capacity	$ 26.3	$ 0.6		$ 50.0
Maximum borrowing capacity					85.0			85.0
Capitalized financing fees written off			1.0						0.4	0.4
Number of days within which letters of credit reduce to zero	90 days
Credit facility termination date		Jan. 21, 2014
New Canadian real estate facilities						5.5	45.7
Maturity date						Nov. 30, 2018	Nov. 30, 2018
Debt Instruments, term							7 years	3 years