Securities - Securities Available for Sale (Detail) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 7,434,480	$ 7,777,950
Gross Unrealized Gains	1,608	1,790
Gross Unrealized Losses	(767,473)	(773,393)
Securities available for sale	6,668,615	7,006,347
U.S. Treasury [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	810,770	804,158
Gross Unrealized Gains		58
Gross Unrealized Losses	(22,946)	(27,146)
Securities available for sale	787,824	777,070
U.S. Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	178,112	178,261
Gross Unrealized Losses	(5,811)	(6,965)
Securities available for sale	172,301	171,296
Mortgage-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,307,758	4,574,905
Gross Unrealized Gains	49	92
Gross Unrealized Losses	(594,987)	(592,875)
Securities available for sale	3,712,820	3,982,122
State and political subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,399,314	1,465,598
Gross Unrealized Gains	1,341	1,608
Gross Unrealized Losses	(96,960)	(104,799)
Securities available for sale	1,303,695	1,362,407
Corporates [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	384,855	401,059
Gross Unrealized Losses	(42,199)	(33,559)
Securities available for sale	342,656	367,500
Collateralized loan obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	353,671	353,969
Gross Unrealized Gains	218	32
Gross Unrealized Losses	(4,570)	(8,049)
Securities available for sale	$ 349,319	$ 345,952

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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