Income taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Oct. 31, 2014	Nov. 01, 2013	Oct. 31, 2014	Nov. 01, 2013
Income taxes
Reserves for uncertain tax benefits	$ 9.4		$ 9.4
Interest accrued related to uncertain tax benefits	0.8		0.8
Potential penalties accrued related to uncertain tax benefits	0.4		0.4
Aggregate reserve for uncertain tax positions including interest and penalties	10.6		10.6
Reserves for uncertain tax benefits included in current liabilities as Accrued expenses and other	0.2		0.2
Reserves for uncertain tax benefits included in noncurrent Other liabilities	10.4		10.4
Reserve for uncertain tax positions for which a reduction is reasonably possible in the next twelve months	3.2		3.2
Reserve for uncertain tax positions that would impact effective tax rate if recognized	$ 9.4		$ 9.4
Effective income tax rates (as a percent)	36.50%	35.60%	37.50%	36.80%