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Commitments and contingencies - Additional information (Details)
$ / shares in Units, shares in Millions, $ in Millions
Aug. 12, 2016
USD ($)
Aug. 01, 2016
employee
Aug. 12, 2015
$ / shares
Oct. 29, 2016
lawsuit
shares
Aug. 01, 2015
USD ($)
Mar. 25, 2014
lawsuit
Loss Contingencies [Line Items]            
Common stock appraisal demanded and not withdrawn (shares) | shares       8.8    
Zale Corporation            
Loss Contingencies [Line Items]            
Pending claims | lawsuit       3   5
Zale Corporation            
Loss Contingencies [Line Items]            
Consideration received by acquiree shareholders (in dollars per share) | $ / shares     $ 21.00      
Loss contingency accrual, provision $ 34.2          
Loss contingency, accrual, current         $ 34.2  
EPA Collective Action            
Loss Contingencies [Line Items]            
Number of employees opted in lawsuit | employee   10,345