Securities - Securities Available for Sale (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 7,248,525	$ 7,777,950
Gross Unrealized Gains	587	1,790
Gross Unrealized Losses	(918,413)	(773,393)
Securities available for sale	6,330,699	7,006,347
U.S. Treasury [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	797,238	804,158
Gross Unrealized Gains		58
Gross Unrealized Losses	(17,863)	(27,146)
Securities available for sale	779,375	777,070
U.S. Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	178,037	178,261
Gross Unrealized Losses	(4,687)	(6,965)
Securities available for sale	173,350	171,296
Mortgage-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,175,240	4,574,905
Gross Unrealized Gains		92
Gross Unrealized Losses	(695,289)	(592,875)
Securities available for sale	3,479,951	3,982,122
State and political subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,367,097	1,465,598
Gross Unrealized Gains	51	1,608
Gross Unrealized Losses	(160,492)	(104,799)
Securities available for sale	1,206,656	1,362,407
Corporates [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	382,914	401,059
Gross Unrealized Losses	(38,013)	(33,559)
Securities available for sale	344,901	367,500
Collateralized loan obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	347,999	353,969
Gross Unrealized Gains	536	32
Gross Unrealized Losses	(2,069)	(8,049)
Securities available for sale	$ 346,466	$ 345,952