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Commitments and contingent liabilities - Additional Information (Detail) - USD ($)
9 Months Ended
Dec. 05, 2014
Sep. 27, 2015
Loss Contingencies [Line Items]    
Estimated litigation liability   $ 2,700,000
Parish of Calcasieu | Judicial Ruling | Compensatory Damages    
Loss Contingencies [Line Items]    
Damages awarded $ 100,000  
Parish of Calcasieu | Judicial Ruling | Punitive Damages    
Loss Contingencies [Line Items]    
Damages awarded $ 23,000,000  
Parish of Calcasieu | Judicial Ruling | Unfavorable Regulatory Action    
Loss Contingencies [Line Items]    
Possible loss   10,000,000.0
Discontinued Operations    
Loss Contingencies [Line Items]    
Estimated litigation liability   $ 1,500,000
Minimum    
Loss Contingencies [Line Items]    
Time-frame over which the accrued amounts may be paid out, in years   15 years
Maximum    
Loss Contingencies [Line Items]    
Time-frame over which the accrued amounts may be paid out, in years   20 years
Accrued Liabilities    
Loss Contingencies [Line Items]    
Waste disposed accrued liability   $ 1,200,000
Other Liability    
Loss Contingencies [Line Items]    
Waste disposed accrued liability   $ 6,200,000