Commitments and contingent liabilities (Detail) - USD ($) $ in Millions		3 Months Ended
	Feb. 17, 2021	Mar. 28, 2021
Loss Contingencies [Line Items]
Estimated litigation liability		$ 0.4
Pending Litigation
Loss Contingencies [Line Items]
Money damages sought	$ 66.9
Minimum
Loss Contingencies [Line Items]
Estimated time frame over which accrued amounts may be paid out		10 years
Maximum
Loss Contingencies [Line Items]
Estimated time frame over which accrued amounts may be paid out		15 years
Accrued Liabilities
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies		$ 1.6
Other Liability
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies		$ 5.0