| Summary of significant accounting policies - Insurance Expense (Details) $ in Thousands | 12 Months Ended | 
|---|---|
| Feb. 01, 2020  USD ($) | |
| Summary of significant accounting policies | |
| Stop loss coverage per employee health claim | $ 350 | 
| Stop loss coverage per general liability claim | 100 | 
| Stop loss coverage per workers compensation claim | $ 250 | 
| X | ||||||||||
| 
- Definition Stop loss coverage of employee health claims. No definition available. 
 | 
| X | ||||||||||
| 
- Definition Stop loss coverage of general liability claims. No definition available. 
 | 
| X | ||||||||||
| 
- Definition Stop loss coverage of workers compensation claims. No definition available. 
 | 
| X | ||||||||||
| 
- References No definition available. 
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