Income taxes - Additional Information (Detail) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013 USD ($)	Dec. 31, 2013 Canada [Member] USD ($)	Dec. 31, 2013 Canada [Member] CAD
Income Tax Examination [Line Items]
Net operating loss carry forwards utilized on sale of SCO	$ 17.6
Capital loss from sale of business			(85.6)
Valuation allowance recorded for capital losses		21.7
Capital loss utilized			3.7
Capital losses carry back period		3 years	3 years
Tax benefit recognized as a result of allowable carry back		0.5
Valuation allowance recorded	20.5
Net operating loss carry forward			2.6
Net operating loss expiration period range start		2032	2032
Net operating loss expiration period range end		2033	2033