v3.26.1
Securities - Gross Unrealized Losses and Fair Value of Investment Securities Held to Maturity (Detail)
$ in Thousands
Jun. 30, 2026
USD ($)
Security
Dec. 31, 2025
USD ($)
Security
Schedule Of Held To Maturity Securities [Line Items]    
Less than 12 months, Count | Security 204 159
Less than 12 months, Fair Value $ 1,060,928 $ 850,159
Less than 12 months,Unrealized Losses $ (46,874) $ (42,077)
12 months or more, Count | Security 1,603 1,616
12 months or more, Fair Value $ 3,278,027 $ 3,479,693
12 months or more, Unrealized Losses $ (453,889) $ (458,760)
Total Count | Security 1,807 1,775
Total Fair Value $ 4,338,955 $ 4,329,852
Total Unrealized Losses $ (500,763) $ (500,837)
U.S. Treasury [Member]    
Schedule Of Held To Maturity Securities [Line Items]    
Less than 12 months, Count | Security 7 3
Less than 12 months, Fair Value $ 37,705 $ 15,913
Less than 12 months,Unrealized Losses $ (555) $ (37)
Total Count | Security 7 3
Total Fair Value $ 37,705 $ 15,913
Total Unrealized Losses $ (555) $ (37)
Mortgage-backed [Member]    
Schedule Of Held To Maturity Securities [Line Items]    
Less than 12 months, Count | Security 17 10
Less than 12 months, Fair Value $ 195,205 $ 147,066
Less than 12 months,Unrealized Losses $ (3,487) $ (918)
12 months or more, Count | Security 262 262
12 months or more, Fair Value $ 1,890,512 $ 1,998,984
12 months or more, Unrealized Losses $ (315,967) $ (304,122)
Total Count | Security 279 272
Total Fair Value $ 2,085,717 $ 2,146,050
Total Unrealized Losses $ (319,454) $ (305,040)
State and political subdivisions [Member]    
Schedule Of Held To Maturity Securities [Line Items]    
Less than 12 months, Count | Security 180 146
Less than 12 months, Fair Value $ 828,018 $ 687,180
Less than 12 months,Unrealized Losses $ (42,832) $ (41,122)
12 months or more, Count | Security 1,341 1,354
12 months or more, Fair Value $ 1,387,515 $ 1,480,709
12 months or more, Unrealized Losses $ (137,922) $ (154,638)
Total Count | Security 1,521 1,500
Total Fair Value $ 2,215,533 $ 2,167,889
Total Unrealized Losses $ (180,754) $ (195,760)