Accumulated Other Comprehensive (Loss) Income, Net of Tax (Schedule of Other Comprehensive Income (Loss)) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ 8,689,996	$ 8,056,186
Other comprehensive (loss) income before reclassifications	(75,432)	80,970
Amounts reclassified from accumulated other comprehensive (loss)	9,902	15,970
Other comprehensive (loss) income, net of tax	(65,530)	96,940
Ending Balance	8,747,498	8,294,294
Available For Sale and Transferred Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(517,450)	(631,160)
Other comprehensive (loss) income before reclassifications	(45,392)	56,635
Amounts reclassified from accumulated other comprehensive (loss)	9,121	14,983
Other comprehensive (loss) income, net of tax	(36,271)	71,618
Ending Balance	(553,721)	(559,542)
Derivative Instruments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(2,869)	(8,874)
Other comprehensive (loss) income before reclassifications	(30,291)	20,782
Amounts reclassified from accumulated other comprehensive (loss)	302	592
Other comprehensive (loss) income, net of tax	(29,989)	21,374
Ending Balance	(32,858)	12,500
Defined Benefit Pension and Other Postretirement Benefit Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(30,252)	(44,926)
Other comprehensive (loss) income before reclassifications	251	3,553
Amounts reclassified from accumulated other comprehensive (loss)	479	395
Other comprehensive (loss) income, net of tax	730	3,948
Ending Balance	(29,522)	(40,978)
Accumulated Other Comprehensive Income (Loss), Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(550,571)	(684,960)
Other comprehensive (loss) income, net of tax	(65,530)	96,940
Ending Balance	$ (616,101)	$ (588,020)