Commitments and contingent liabilities - Additional Information (Detail) - USD ($)		12 Months Ended
	Dec. 05, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Loss Contingencies [Line Items]
Operating leases, rental expense		$ 34,600,000	$ 29,400,000	$ 26,400,000
Discontinued Operations
Loss Contingencies [Line Items]
Contingency reserve for litigation		$ 1,500,000	2,400,000
Minimum
Loss Contingencies [Line Items]
Time-frame over which the accrued amounts may be paid out, in years		P15Y
Maximum
Loss Contingencies [Line Items]
Time-frame over which the accrued amounts may be paid out, in years		P20Y
Accrued Liabilities
Loss Contingencies [Line Items]
Waste disposed accrued liability		$ 1,200,000	1,300,000
Contingency reserve for litigation		2,500,000	6,000,000
Other Liability
Loss Contingencies [Line Items]
Waste disposed accrued liability		6,100,000	$ 6,500,000
Parish of Calcasieu | Judicial Ruling | Compensatory Damages
Loss Contingencies [Line Items]
Damages awarded to plaintiff	$ 100,000
Parish of Calcasieu | Judicial Ruling | Punitive Damages
Loss Contingencies [Line Items]
Damages awarded to plaintiff	$ 23,000,000
Parish of Calcasieu | Judicial Ruling | Unfavorable Regulatory Action
Loss Contingencies [Line Items]
Range of possible loss, maximum		$ 10,000,000