Accumulated Other Comprehensive Earnings (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 29, 2018	Sep. 30, 2017	Sep. 29, 2018	Sep. 30, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balances at Beginning of Period	$ (70,679)	$ 27,948	$ 152,636	$ 23,427
Unrealized (loss) on debt securities in 2018. Unrealized gain on debt and equity securities in 2017.	(2,076)	49,043	(28,657)	111,585
Net realized (gain) loss on debt securities reclassified to investment income in 2018. Net realized (gain) on debt and equity securities reclassified to investment income in 2017.	(181)	(6,334)	266	(64,355)
Amortization of actuarial loss reclassified to other nonoperating income, net	564	0	1,693	0
Net other comprehensive (losses) earnings	(1,693)	42,709	(26,698)	47,230
Cumulative effect of net unrealized gain on equity securities reclassified to retained earnings			(198,310)
Balances at End of Period	(72,372)	70,657	(72,372)	70,657
AFS Securities [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balances at Beginning of Period	(56,387)	33,639	168,057	29,118
Unrealized (loss) on debt securities in 2018. Unrealized gain on debt and equity securities in 2017.	(2,076)	49,043	(28,657)	111,585
Net realized (gain) loss on debt securities reclassified to investment income in 2018. Net realized (gain) on debt and equity securities reclassified to investment income in 2017.	(181)	(6,334)	266	(64,355)
Net other comprehensive (losses) earnings	(2,257)	42,709	(28,391)	47,230
Cumulative effect of net unrealized gain on equity securities reclassified to retained earnings			(198,310)
Balances at End of Period	(58,644)	76,348	(58,644)	76,348
Postretirement Benefits [Member}
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balances at Beginning of Period	(14,292)	(5,691)	(15,421)	(5,691)
Amortization of actuarial loss reclassified to other nonoperating income, net	564	0	1,693	0
Net other comprehensive (losses) earnings	564	0	1,693	0
Balances at End of Period	$ (13,728)	$ (5,691)	$ (13,728)	$ (5,691)

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

No definition available.

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

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