Income taxes (Details) - USD ($) $ in Millions	3 Months Ended
	May 04, 2018	May 05, 2017
Income taxes
Reserves for uncertain tax benefits	$ 1.1
Interest accrued related to uncertain tax benefits	0.7
Potential penalties accrued related to uncertain tax benefits	0.8
Reserves for uncertain tax benefits included in noncurrent Other liabilities	2.6
Reserve for uncertain tax positions that would impact effective tax rate if recognized	$ 1.1
Effective income tax rates (as a percent)	21.60%	37.20%
U.S. federal statutory rate on earnings before income taxes (as a percent)	21.00%	35.00%