Subsequent events (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Jan. 31, 2014 Segments	Jan. 31, 2013 Segments
Subsequent Event [Line Items]
Subsequent Event, Date		Apr. 26, 2013
Disposal Date		Apr. 30, 2013
Estimated taxable gain on disposition of assets		$ 11.6
Change in deferred tax assets valuation allowance	$ 3.0	$ 12.5
Number of reportable segments	2	3