Other Comprehensive Income (Schedule of Accumulated Other Comprehensive Income, Net of Tax) (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	$ 347,318
Net other comprehensive income (loss) during period	(1,695,612)	$ (165,652)	$ 245,600
Ending Balance	(1,348,294)	347,318
Available-for-sale Securities [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	380,209	563,801	313,304
Other comprehensive income (loss) before reclassification	(1,694,000)	(183,537)	336,598
Reclassification of amounts included in net income	0	(55)	(86,101)
Net other comprehensive income (loss) during period	(1,694,000)	(183,592)	250,497
Ending Balance	(1,313,791)	380,209	563,801
Defined Benefit Plans [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	(32,891)	(50,831)	(45,934)
Other comprehensive income (loss) before reclassification	(3,954)	13,108	(9,099)
Reclassification of amounts included in net income	2,342	4,832	4,202
Net other comprehensive income (loss) during period	(1,612)	17,940	(4,897)
Ending Balance	(34,503)	(32,891)	(50,831)
AOCI Attributable to Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	347,318	512,970	267,370
Other comprehensive income (loss) before reclassification	(1,697,954)	(170,429)	327,499
Reclassification of amounts included in net income	2,342	4,777	(81,899)
Net other comprehensive income (loss) during period	(1,695,612)	(165,652)	245,600
Ending Balance	$ (1,348,294)	$ 347,318	$ 512,970

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.

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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+ Details