Securities - Gross Unrealized Losses and Fair Value of Investment Securities Held to Maturity (Detail) $ in Thousands	Jun. 30, 2024 USD ($) Security	Dec. 31, 2023 USD ($) Security
Schedule Of Held To Maturity Securities [Line Items]
Less than 12 months, Count | Security	60	148
Less than 12 months, Fair Value	$ 275,647	$ 572,419
Less than 12 months,Unrealized Losses	$ (13,300)	$ (22,571)
12 months or more, Count | Security	1,707	1,617
12 months or more, Fair Value	$ 4,173,529	$ 4,110,888
12 months or more, Unrealized Losses	$ (636,821)	$ (506,969)
Total Count | Security	1,767	1,765
Total Fair Value	$ 4,449,176	$ 4,683,307
Total Unrealized Losses	$ (650,121)	$ (529,540)
U.S. Agencies [Member]
Schedule Of Held To Maturity Securities [Line Items]
12 months or more, Count | Security	10	11
12 months or more, Fair Value	$ 113,997	$ 120,524
12 months or more, Unrealized Losses	$ (2,273)	$ (2,686)
Total Count | Security	10	11
Total Fair Value	$ 113,997	$ 120,524
Total Unrealized Losses	$ (2,273)	$ (2,686)
Mortgage-backed [Member]
Schedule Of Held To Maturity Securities [Line Items]
Less than 12 months, Count | Security	4	2
Less than 12 months, Fair Value	$ 2,141	$ 1,469
Less than 12 months,Unrealized Losses	$ (47)	$ (14)
12 months or more, Count | Security	265	263
12 months or more, Fair Value	$ 2,208,664	$ 2,377,922
12 months or more, Unrealized Losses	$ (421,809)	$ (356,643)
Total Count | Security	269	265
Total Fair Value	$ 2,210,805	$ 2,379,391
Total Unrealized Losses	$ (421,856)	$ (356,657)
State and political subdivisions [Member]
Schedule Of Held To Maturity Securities [Line Items]
Less than 12 months, Count | Security	56	146
Less than 12 months, Fair Value	$ 273,506	$ 570,950
Less than 12 months,Unrealized Losses	$ (13,253)	$ (22,557)
12 months or more, Count | Security	1,432	1,343
12 months or more, Fair Value	$ 1,850,868	$ 1,612,442
12 months or more, Unrealized Losses	$ (212,739)	$ (147,640)
Total Count | Security	1,488	1,489
Total Fair Value	$ 2,124,374	$ 2,183,392
Total Unrealized Losses	$ (225,992)	$ (170,197)