Organization and principal accounting policies - Additional information (Details)	3 Months Ended
	Apr. 29, 2017 segment
Property, Plant and Equipment [Line Items]
Number of reportable segments	5
Seasonal revenues, first quarter sales, percent	20.00%
SSeasonal revenues, second quarter sales, percent	20.00%
Seasonal revenues, third quarter sales, percent	20.00%
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%