Organization and principal accounting policies - Additional information (Details)	3 Months Ended
	May 05, 2018 segment
Property, Plant and Equipment [Line Items]
Number of reportable segments	3
Seasonal revenues, fourth quarter sales, percent	40.00%
UK Jewelry and Zales Jewelry | Minimum
Property, Plant and Equipment [Line Items]
Operating income expected in fourth quarter, Percent	45.00%
UK Jewelry and Zales Jewelry | Maximum
Property, Plant and Equipment [Line Items]
Operating income expected in fourth quarter, Percent	55.00%
Sterling Jewelers | Minimum
Property, Plant and Equipment [Line Items]
Operating income expected in fourth quarter, Percent	40.00%
Sterling Jewelers | Maximum
Property, Plant and Equipment [Line Items]
Operating income expected in fourth quarter, Percent	45.00%