Other Comprehensive Income - Schedule of Accumulated Other Comprehensive Income, Net of Tax (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	$ (1,348,294)
Other comprehensive income (loss), net of tax	206,156	$ (719,108)
Ending Balance	(1,142,138)
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	205,486	(719,693)
Reclassification of amounts included in net income	(17)	0
Other comprehensive income (loss), net of tax	205,469	(719,693)
Ending Balance	(1,108,322)	(339,484)
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	687	585
Other comprehensive income (loss), net of tax	687	585
Ending Balance	(33,816)	(32,306)
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	205,486	(719,693)
Reclassification of amounts included in net income	670	585
Other comprehensive income (loss), net of tax	206,156	(719,108)
Ending Balance	$ (1,142,138)	$ (371,790)