Accumulated Other Comprehensive Earnings (Losses) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 25, 2022	Jun. 26, 2021	Jun. 25, 2022	Jun. 26, 2021
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balances at Beginning of Period	$ (380,552)	$ 93,199	$ (5,421)	$ 200,951
Unrealized (loss) gain on debt securities	(175,084)	12,977	(549,727)	(90,571)
Net realized gain on debt securities reclassified to investment income	(82)	(3,333)	(908)	(8,916)
Adjustment to postretirement benefit obligation	339	1,380	677	2,759
Net other comprehensive (losses) earnings	(174,827)	11,024	(549,958)	(96,728)
Balances at End of Period	(555,379)	104,223	(555,379)	104,223
Investments [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balances at Beginning of Period	(368,415)	114,773	7,054	223,904
Unrealized (loss) gain on debt securities	(175,084)	12,977	(549,727)	(90,571)
Net realized gain on debt securities reclassified to investment income	(82)	(3,333)	(908)	(8,916)
Net other comprehensive (losses) earnings	(175,166)	9,644	(550,635)	(99,487)
Balances at End of Period	(543,581)	124,417	(543,581)	124,417
Postretirement Benefit Obligation [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balances at Beginning of Period	(12,137)	(21,574)	(12,475)	(22,953)
Adjustment to postretirement benefit obligation	339	1,380	677	2,759
Net other comprehensive (losses) earnings	339	1,380	677	2,759
Balances at End of Period	$ (11,798)	$ (20,194)	$ (11,798)	$ (20,194)