v3.26.1
Securities - Continuous Unrealized-Loss Position of Available-for-Sale Securities (Detail) - USD ($)
$ in Thousands
Jun. 30, 2026
Dec. 31, 2025
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Fair Value $ 1,299,577 $ 262,784
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss (15,373) (1,107)
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value 3,296,750 3,634,994
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss (361,418) (372,454)
Available-for-sale securities, continuous unrealized loss position, Fair Value 4,596,327 3,897,778
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss (376,791) (373,561)
U.S. Treasury Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Fair Value   0
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss   0
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value   59,815
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss   (324)
Available-for-sale securities, continuous unrealized loss position, Fair Value   59,815
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss   (324)
Obligations of State and Political Subdivisions [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Fair Value 18,352 6,245
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss (323) (387)
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value 1,343,052 1,363,145
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss (92,710) (113,510)
Available-for-sale securities, continuous unrealized loss position, Fair Value 1,361,404 1,369,390
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss (93,033) (113,897)
Residential Mortgage-Backed Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Fair Value 575,326 63,311
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss (8,188) (120)
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value 1,761,550 1,996,200
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss (263,003) (252,955)
Available-for-sale securities, continuous unrealized loss position, Fair Value 2,336,876 2,059,511
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss (271,191) (253,075)
Commercial Mortgage-Backed Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Fair Value 691,019 188,241
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss (6,819) (599)
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value 139,055 152,452
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss (2,553) (2,531)
Available-for-sale securities, continuous unrealized loss position, Fair Value 830,074 340,693
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss (9,372) (3,130)
Corporate Bonds and Other [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Fair Value 14,880 4,987
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss (43) (1)
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value 53,093 63,382
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss (3,152) (3,134)
Available-for-sale securities, continuous unrealized loss position, Fair Value 67,973 68,369
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss $ (3,195) $ (3,135)