Accumulated Other Comprehensive Earnings (Losses) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 24, 2022	Sep. 25, 2021	Sep. 24, 2022	Sep. 25, 2021
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balances at Beginning of Period	$ (555,379)	$ 104,223	$ (5,421)	$ 200,951
Unrealized loss on debt securities	(119,057)	(12,611)	(668,784)	(103,182)
Net realized loss (gain) on debt securities reclassified to investment income	1,889	(6,258)	981	(15,174)
Adjustment to postretirement benefit obligation	339	1,378	1,016	4,137
Net other comprehensive (losses) earnings	(116,829)	(17,491)	(666,787)	(114,219)
Balances at End of Period	(672,208)	86,732	(672,208)	86,732
Investments [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balances at Beginning of Period	(543,581)	124,417	7,054	223,904
Unrealized loss on debt securities	(119,057)	(12,611)	(668,784)	(103,182)
Net realized loss (gain) on debt securities reclassified to investment income	1,889	(6,258)	981	(15,174)
Net other comprehensive (losses) earnings	(117,168)	(18,869)	(667,803)	(118,356)
Balances at End of Period	(660,749)	105,548	(660,749)	105,548
Postretirement Benefit Obligation [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balances at Beginning of Period	(11,798)	(20,194)	(12,475)	(22,953)
Adjustment to postretirement benefit obligation	339	1,378	1,016	4,137
Net other comprehensive (losses) earnings	339	1,378	1,016	4,137
Balances at End of Period	$ (11,459)	$ (18,816)	$ (11,459)	$ (18,816)