Commitments and contingent liabilities (Detail) $ in Millions	6 Months Ended
	Jun. 30, 2019 USD ($)
Loss Contingencies [Line Items]
Estimated litigation liability	$ 0.2
Minimum
Loss Contingencies [Line Items]
Estimated time fram over which accrued amounts may be paid out	10 years
Maximum
Loss Contingencies [Line Items]
Estimated time fram over which accrued amounts may be paid out	15 years
Accrued Liabilities
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies	$ 0.9
Other Liability
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies	$ 6.4