Consolidated Statements of Comprehensive Earnings (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
Dec. 28, 2019	Dec. 29, 2018	Dec. 30, 2017
Statement of Comprehensive Income [Abstract]
Unrealized gain (loss) on debt securities net of income taxes in 2019 and 2018. Unrealized gain on debt and equity securities net of income taxes in 2017.	$ 50,504	$ (6,521)	$ 110,818
Reclassification adjustment for net realized (gain) loss on debt securities net of income taxes in 2019 and 2018. Reclassification adjustment for net realized (gain) on debt and equity securities net of income taxes in 2017.	(205)	118	(42,088)
Adjustment to postretirement benefit obligation net of income taxes in 2019, 2018 and 2017.	$ (3,576)	$ 2,963	$ (4,406)

Amount, after reclassification adjustment, of tax (expense) benefit for (increase) decrease in accumulated other comprehensive income of defined benefit plan.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=118930883&loc=d3e640-108580

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 10A
-Subparagraph (i-k)
-URI http://asc.fasb.org/extlink&oid=118930883&loc=SL7669646-108580

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 45
-Paragraph 19
-URI http://asc.fasb.org/extlink&oid=108774443&loc=SL4569616-111683

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

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