Securities - Schedule of Amortized Cost, Fair Value and Gross Unrealized Gains and Losses for Securities Held to Maturity (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	$ 5,732,583	$ 5,861,599
Gross Unrealized Gains	6,834	17,629
Gross Unrealized Losses	(882,951)	(598,569)
Held to Maturity, Fair value	4,856,466	5,280,659
Allowance for Credit Losses	(2,886)	(2,407)
Net Carrying Amount	5,729,697	5,859,192
U.S. Agencies [Member]
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	123,180	123,091
Gross Unrealized Losses	(4,228)	(4,567)
Held to Maturity, Fair value	118,952	118,524
Net Carrying Amount	123,180	123,091
Mortgage-backed [Member]
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	2,790,103	2,965,586
Gross Unrealized Gains		11
Gross Unrealized Losses	(512,431)	(392,530)
Held to Maturity, Fair value	2,277,672	2,573,067
Net Carrying Amount	2,790,103	2,965,586
State and political subdivisions [Member]
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	2,819,300	2,772,922
Gross Unrealized Gains	6,834	17,618
Gross Unrealized Losses	(366,292)	(201,472)
Held to Maturity, Fair value	2,459,842	2,589,068
Allowance for Credit Losses	(2,886)	(2,407)
Net Carrying Amount	$ 2,816,414	$ 2,770,515