Commitments and contingent liabilities - Additional Information (Detail) - USD ($) $ in Millions		12 Months Ended
	Dec. 05, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Loss Contingencies [Line Items]
Operating leases, rental expense		$ 34.0	$ 34.6	$ 29.4
Discontinued Operations
Loss Contingencies [Line Items]
Contingency reserve for litigation		$ 1.6	1.5
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		$ 1.1	1.2
Contingency reserve for litigation		2.5	2.5
Other Liability
Loss Contingencies [Line Items]
Waste disposed accrued liability		5.8	$ 6.1
Parish of Calcasieu | Judicial Ruling | Compensatory Damages
Loss Contingencies [Line Items]
Damages awarded to plaintiff	$ 0.1
Parish of Calcasieu | Judicial Ruling | Punitive Damages
Loss Contingencies [Line Items]
Damages awarded to plaintiff	$ 23.0
Parish of Calcasieu | Judicial Ruling | Unfavorable Regulatory Action | Maximum
Loss Contingencies [Line Items]
Range of possible loss		$ 10.0