Commitments and contingencies - Changes in Accrued Environmental Remediation and Related Costs (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Commitments and contingencies.
Balance at the beginning of the period	$ 92,358	$ 92,940	$ 93,416
Environmental Loss Contingency, Statement of Financial Position [Extensible Enumeration]	Current liability, Noncurrent liability	Current liability, Noncurrent liability	Current liability, Noncurrent liability
Additions charged to expense, net	$ 558	$ 486	$ 788
Payments, net	(1,810)	(1,068)	(1,264)
Balance at the end of the period	91,106	92,358	92,940
Amounts recognized in the balance sheet:
Current liability	1,655	2,627	2,643
Noncurrent liability	$ 89,451	$ 89,731	$ 90,297