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Share-based compensation - Additional Information (Details) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Aug. 03, 2019
Aug. 04, 2018
Aug. 03, 2019
Aug. 04, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]        
Share-based compensation expense $ 4.3 $ 6.4 $ 8.3 $ 8.2