Other Comprehensive Income - Schedule of Accumulated Other Comprehensive Income, Net of Tax (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance			$ (1,348,294)
Other comprehensive income (loss), net of tax	$ (473,800)	$ (654,719)	(430,533)	$ (1,876,243)
Ending Balance	(1,778,827)		(1,778,827)
Securities Available For Sale [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance			(1,313,791)	380,209
Other comprehensive income (loss) before reclassifications			(432,542)	(1,877,999)
Reclassification of amounts included in net income			(52)	0
Other comprehensive income (loss), net of tax			(432,594)	(1,877,999)
Ending Balance	(1,746,385)	(1,497,790)	(1,746,385)	(1,497,790)
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance			(34,503)	(32,891)
Other comprehensive income (loss) before reclassifications			0	0
Reclassification of amounts included in net income			2,061	1,756
Other comprehensive income (loss), net of tax			2,061	1,756
Ending Balance	(32,442)	(31,135)	(32,442)	(31,135)
AOCI Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance			(1,348,294)	347,318
Other comprehensive income (loss) before reclassifications			(432,542)	(1,877,999)
Reclassification of amounts included in net income			2,009	1,756
Other comprehensive income (loss), net of tax			(430,533)	(1,876,243)
Ending Balance	$ (1,778,827)	$ (1,528,925)	$ (1,778,827)	$ (1,528,925)