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Income taxes - Reconciliation of Statutory Tax Rate to Effective Tax Rate (Details)
9 Months Ended
Nov. 02, 2019
Nov. 03, 2018
Income Tax Disclosure [Abstract]    
Estimated annual effective tax rate before discrete items 13.60% 22.70%
Discrete items recognized (9.30%) (0.20%)
Effective tax rate recognized in statement of operations 4.30% 22.50%