Accumulated Other Comprehensive Earnings (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 29, 2019	Jun. 30, 2018	Jun. 29, 2019	Jun. 30, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balances at Beginning of Period	$ 4,052	$ (69,068)	$ (55,762)	$ 152,636
Unrealized gain (loss) on debt securities in 2019 and 2018, respectively.	58,130	(2,600)	117,651	(26,581)
Net realized loss on debt securities reclassified to investment income in 2019 and 2018, respectively.	37	425	330	447
Adjustment to postretirement benefit obligation	0	564	0	1,129
Net other comprehensive earnings (losses)	58,167	(1,611)	117,981	(25,005)
Cumulative effect of net unrealized gain on equity securities reclassified to retained earnings	0	0	0	(198,310)
Balances at End of Period	62,219	(70,679)	62,219	(70,679)
AFS Securities [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balances at Beginning of Period	10,781	(54,212)	(49,033)	168,057
Unrealized gain (loss) on debt securities in 2019 and 2018, respectively.	58,130	(2,600)	117,651	(26,581)
Net realized loss on debt securities reclassified to investment income in 2019 and 2018, respectively.	37	425	330	447
Net other comprehensive earnings (losses)	58,167	(2,175)	117,981	(26,134)
Cumulative effect of net unrealized gain on equity securities reclassified to retained earnings	0	0	0	(198,310)
Balances at End of Period	68,948	(56,387)	68,948	(56,387)
Postretirement Benefits [Member}
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balances at Beginning of Period	(6,729)	(14,856)	(6,729)	(15,421)
Adjustment to postretirement benefit obligation	0	564	0	1,129
Net other comprehensive earnings (losses)	0	564	0	1,129
Balances at End of Period	$ (6,729)	$ (14,292)	$ (6,729)	$ (14,292)

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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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.

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Amount of the cumulative effect on retained earnings net of related income tax effect.

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

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Amount after tax of reclassification adjustment from accumulated other comprehensive income for unrealized gain (loss) realized upon the sale of available-for-sale securities.

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

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Amount after tax, before reclassification adjustments, of unrealized holding gain (loss) on available-for-sale securities.

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