Other Comprehensive Income (Schedule of Accumulated Other Comprehensive Income, Net of Tax) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	$ (1,252,004)
Net other comprehensive income (loss) during period	409,053	$ (132,785)	$ 229,075
Ending Balance	(842,951)	(1,252,004)
Available-for-sale Securities [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	(1,230,828)	(1,094,794)	(1,313,791)
Other comprehensive income (loss) before reclassification	406,088	(136,110)	219,049
Reclassification of amounts included in net income	671	76	(52)
Net other comprehensive income (loss) during period	406,759	(136,034)	218,997
Ending Balance	(824,069)	(1,230,828)	(1,094,794)
Defined Benefit Plans [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	(21,176)	(24,425)	(34,503)
Other comprehensive income (loss) before reclassification	1,315	1,927	7,330
Reclassification of amounts included in net income	979	1,322	2,748
Net other comprehensive income (loss) during period	2,294	3,249	10,078
Ending Balance	(18,882)	(21,176)	(24,425)
AOCI Attributable to Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	(1,252,004)	(1,119,219)	(1,348,294)
Other comprehensive income (loss) before reclassification	407,403	(134,183)	226,379
Reclassification of amounts included in net income	1,650	1,398	2,696
Net other comprehensive income (loss) during period	409,053	(132,785)	229,075
Ending Balance	$ (842,951)	$ (1,252,004)	$ (1,119,219)