Commitments and contingencies - Changes in Accrued Environmental Remediation and Related Costs (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Commitments and contingencies.
Balance at the beginning of the period	$ 91,106
Additions charged to expense, net	170
Payments, net	(329)
Balance at the end of the period	90,947
Amounts recognized in the balance sheet:
Current liability	1,584	$ 1,655
Noncurrent liability	$ 89,363	$ 89,451