Accumulated Other Comprehensive Earnings (Losses) (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 26, 2022	Mar. 27, 2021
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balances at Beginning of Period	$ (5,421)	$ 200,951
Unrealized loss on debt securities	(374,643)	(103,548)
Net realized gain on debt securities reclassified to investment income	(826)	(5,583)
Adjustment to postretirement benefit obligation	338	1,379
Net other comprehensive (losses) earnings	(375,131)	(107,752)
Balances at End of Period	(380,552)	93,199
Investments [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balances at Beginning of Period	7,054	223,904
Unrealized loss on debt securities	(374,643)	(103,548)
Net realized gain on debt securities reclassified to investment income	(826)	(5,583)
Net other comprehensive (losses) earnings	(375,469)	(109,131)
Balances at End of Period	(368,415)	114,773
Postretirement Benefit Obligation [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balances at Beginning of Period	(12,475)	(22,953)
Adjustment to postretirement benefit obligation	338	1,379
Net other comprehensive (losses) earnings	338	1,379
Balances at End of Period	$ (12,137)	$ (21,574)

Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

Amount after tax and reclassification adjustments of other comprehensive income (loss).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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+ Details