Supplemental equity information - Reclassifications of Accumulated Other Comprehensive Loss Related to Postretirement Plans (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 29, 2019	Sep. 30, 2020	Sep. 29, 2019
Equity [Abstract]
Amortization of prior service credit, net	$ 0	$ 0	$ 0	$ 0
Amortization of actuarial gain	(11)	(30)	(36)	(90)
Total reclassifications, before tax	(11)	(30)	(36)	(90)
Income tax expense (benefit)	1	0	(6)	0
Total reclassifications, net of tax	$ (12)	$ (30)	$ (30)	$ (90)

No definition available.

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Amount, before tax, of reclassification adjustment from accumulated other comprehensive (income) loss for prior service cost (credit) of defined benefit plan.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
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Amount, after tax and reclassification adjustment, of (increase) decrease in accumulated other comprehensive income for defined benefit plan.

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Amount, after reclassification adjustment, of tax (expense) benefit for (increase) decrease in accumulated other comprehensive income of defined benefit plan.

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Amount, before tax, of reclassification adjustment from accumulated other comprehensive (income) loss for net period benefit cost (credit) of defined benefit plan.

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Amount, before tax, of reclassification adjustment from accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan.

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