Income taxes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jul. 31, 2015	Aug. 01, 2014	Jul. 31, 2015	Aug. 01, 2014
Income taxes
Reserves for uncertain tax benefits	$ 9.4		$ 9.4
Interest accrued related to uncertain tax benefits	1.1		1.1
Potential penalties accrued related to uncertain tax benefits	0.5		0.5
Aggregate reserve for uncertain tax positions including interest and penalties	11.0		11.0
Reserves for uncertain tax benefits included in noncurrent Other liabilities	11.0		11.0
Reserve for uncertain tax positions for which a reduction is reasonably possible in the next twelve months	3.0		3.0
Reserve for uncertain tax positions that would impact effective tax rate if recognized	$ 9.4		$ 9.4
Effective income tax rates (as a percent)	38.00%	38.10%	37.80%	38.00%