Commitments and contingent liabilities - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Loss Contingencies [Line Items]
Operating leases, rental expense	$ 38.1	$ 36.2	$ 34.0
Minimum
Loss Contingencies [Line Items]
Time-frame over which the accrued amounts may be paid out, in years	P10Y
Maximum
Loss Contingencies [Line Items]
Time-frame over which the accrued amounts may be paid out, in years	P15Y
Accrued Liabilities
Loss Contingencies [Line Items]
Waste disposed accrued liability	$ 0.8	1.0
Contingency reserve for litigation	0.6	3.8
Other Liability
Loss Contingencies [Line Items]
Waste disposed accrued liability	$ 5.6	$ 5.8