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Commitments and contingencies - Narrative (Details)
May 02, 2015
Sep. 24, 2014
Aug. 26, 2014
Jun. 04, 2014
May 28, 2014
lawsuit
Loss Contingencies [Line Items]          
Common stock, shares held by former stockholders (shares)   2,427,000sig_CommonStockSharesHeldByFormerStockholders 2,450,000sig_CommonStockSharesHeldByFormerStockholders 3,904,000sig_CommonStockSharesHeldByFormerStockholders  
Common stock appraisal demanded and not withdrawn (shares) 8,800,000sig_CommonStockAppraisalDemandedAndNotWithdrawnShares        
Zale          
Loss Contingencies [Line Items]          
Pending claims         3us-gaap_LossContingencyPendingClaimsNumber
/ dei_LegalEntityAxis
= sig_ZaleCorporationMember