Commitments and contingent liabilities (Detail) - USD ($)		9 Months Ended
	Dec. 05, 2014	Sep. 25, 2016
Loss Contingencies [Line Items]
Estimated litigation liability		$ 2,500,000
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		$ 1,000,000
Other Liability
Loss Contingencies [Line Items]
Waste disposed accrued liability		5,300,000
Construction In Progress | European Headquarters
Loss Contingencies [Line Items]
Property, plant and equipment		$ 14,600,000