Other Comprehensive Income - Schedule of Accumulated Other Comprehensive Income, Net of Tax (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	$ (1,119,219)
Other comprehensive income (loss), net of tax	(157,064)	$ 206,156
Ending Balance	(1,276,283)
Securities Available For Sale [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(1,094,794)	(1,313,791)
Other comprehensive income (loss) before reclassifications	(157,394)	205,486
Reclassification of amounts included in net income	0	(17)
Other comprehensive income (loss), net of tax	(157,394)	205,469
Ending Balance	(1,252,188)	(1,108,322)
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(24,425)	(34,503)
Other comprehensive income (loss) before reclassifications	0	0
Reclassification of amounts included in net income	330	687
Other comprehensive income (loss), net of tax	330	687
Ending Balance	(24,095)	(33,816)
AOCI Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(1,119,219)	(1,348,294)
Other comprehensive income (loss) before reclassifications	(157,394)	205,486
Reclassification of amounts included in net income	330	670
Other comprehensive income (loss), net of tax	(157,064)	206,156
Ending Balance	$ (1,276,283)	$ (1,142,138)