Employee benefits - Accumulated benefit obligation in excess of plan assets (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	$ 628,175	$ 851,471
Accumulated benefit obligation	628,175	851,471
Fair value of plan assets	619,885	860,484
OPEB Plan
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	118,336	159,958
Accumulated benefit obligation	118,336	159,958
Fair value of plan assets	$ 0	$ 0

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Amount of accumulated benefit obligation for defined benefit plan with accumulated benefit obligation in excess of plan assets.

+ References

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-Publisher FASB
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Amount of plan asset for defined benefit plan with accumulated benefit obligation in excess of plan assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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Amount of projected benefit obligation for defined benefit pension plan with accumulated benefit obligation in excess of plan assets.

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