Employee benefit plans - Component of Net Periodic Pension Cost that are Included in Accumulated Other Comprehensive Loss (Income) (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	$ 11,637
Retirement Plans
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss/(gain)	109,718	$ 114,957
Prior service cost	5,020	5,557
Amount in accumulated other comprehensive loss (income)	114,738	120,514
Retiree Health and Life Insurance Plans
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss/(gain)	(7,706)	(6,120)
Prior service cost	11,251	11,637
Amount in accumulated other comprehensive loss (income)	$ 3,545	$ 5,517

Amount, before tax, of accumulated other comprehensive (income) loss for defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 220
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Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
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-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480506/715-20-50-1

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- Definition

Amount, before tax, of accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit.

+ References

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- Definition

Amount, before tax, of accumulated other comprehensive (income) loss for cost (credit) of benefit change attributable to participants' prior service from plan amendment or plan initiation of defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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