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Income taxes - Reconciliation of Statutory Tax Rate to Effective Tax Rate (Details)
6 Months Ended
Aug. 03, 2019
Aug. 04, 2018
Income Tax Disclosure [Abstract]    
Estimated annual effective tax rate before discrete items(1) 13.70% 32.20%
Discrete items recognized (19.00%) (12.20%)
Effective tax rate recognized in statement of operations (5.30%) 20.00%