Commitments and contingencies - Changes in Accrued Environmental Remediation and Related Costs (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2026	Dec. 31, 2025
Commitments and contingencies.
Balance at the beginning of the period	$ 13,040
Environmental Loss Contingency, Statement of Financial Position [Extensible Enumeration]	Current liability, Noncurrent liability
Additions charged to expense, net	$ 378
Payments, net	(449)
Balance at the end of the period	$ 12,969
Environmental Loss Contingency, Statement of Financial Position [Extensible Enumeration]	Current liability, Noncurrent liability
Amounts recognized in the balance sheet:
Current liability	$ 2,096	$ 2,071
Noncurrent liability	$ 10,873	$ 10,969