Commitments and contingencies - Changes in Accrued Environmental Remediation and Related Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Commitments and contingencies.
Balance at the beginning of the period	$ 69,278	$ 91,106	$ 92,358
Environmental Loss Contingency, Statement of Financial Position [Extensible Enumeration]	Current liability, Noncurrent liability	Current liability, Noncurrent liability	Current liability, Noncurrent liability
Additions (deductions), net	$ 1,885	$ (20,286)	$ 558
Payments, net	(58,123)	(1,542)	(1,810)
Balance at the end of the period	$ 13,040	$ 69,278	$ 91,106
Environmental Loss Contingency, Statement of Financial Position [Extensible Enumeration]	Current liability, Noncurrent liability	Current liability, Noncurrent liability	Current liability, Noncurrent liability
Amounts recognized in the balance sheet:
Current liability	$ 2,071	$ 58,135	$ 1,655
Noncurrent liability	$ 10,969	$ 11,143	$ 89,451