Organization and principal accounting policies - Additional information (Details) $ / shares in Units, $ in Millions		3 Months Ended				9 Months Ended	12 Months Ended
	Oct. 05, 2016 USD ($) $ / shares shares	Jan. 28, 2017	Oct. 29, 2016	Jul. 30, 2016	Apr. 30, 2016	Oct. 29, 2016 segment	Jan. 28, 2017
Property, Plant and Equipment [Line Items]
Number of reportable segments | segment						5
Percent of annual sales			20.00%	20.00%	20.00%
Scenario, Forecast
Property, Plant and Equipment [Line Items]
Percent of annual sales		40.00%
Scenario, Forecast | Minimum
Property, Plant and Equipment [Line Items]
Operating income expected in fourth quarter, Percent							45.00%
Scenario, Forecast | Maximum
Property, Plant and Equipment [Line Items]
Operating income expected in fourth quarter, Percent							55.00%
Scenario, Forecast | Sterling Jewelers | Minimum
Property, Plant and Equipment [Line Items]
Operating income expected in fourth quarter, Percent							40.00%
Scenario, Forecast | Sterling Jewelers | Maximum
Property, Plant and Equipment [Line Items]
Operating income expected in fourth quarter, Percent							45.00%
Series A Redeemable Convertible Preferred Stock
Property, Plant and Equipment [Line Items]
Redeemable convertible preferred stock, shares issued | shares	625,000
Preferred stock, purchase price | $	$ 625.0
Shares issued, price per share | $ / shares	$ 1,000