Summary of significant accounting policies - Fiscal Year (Details)	3 Months Ended								12 Months Ended
	Feb. 03, 2018	Oct. 28, 2017	Jul. 29, 2017	Apr. 29, 2017	Jan. 28, 2017	Oct. 29, 2016	Jul. 30, 2016	Apr. 30, 2016	Feb. 03, 2018	Jan. 28, 2017	Jan. 30, 2016
Summary of significant accounting policies
Fiscal period	98 days	91 days	91 days	91 days	91 days	91 days	91 days	91 days	371 days	364 days	364 days
Minimum
Summary of significant accounting policies
Fiscal period									364 days
Maximum
Summary of significant accounting policies
Fiscal period									371 days