v3.26.1
Securities - Continuous Unrealized-Loss Position of Available-for-Sale Securities (Detail) - USD ($)
$ in Thousands
Mar. 31, 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 $ 920,787 $ 262,784
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss (8,757) (1,107)
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value 3,375,091 3,634,994
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss (379,900) (372,454)
Available-for-sale securities, continuous unrealized loss position, Fair Value 4,295,878 3,897,778
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss (388,657) (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 0
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss 0 0
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value 19,962 59,815
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss (61) (324)
Available-for-sale securities, continuous unrealized loss position, Fair Value 19,962 59,815
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss (61) (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 28,550 6,245
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss (779) (387)
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value 1,324,981 1,363,145
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss (118,819) (113,510)
Available-for-sale securities, continuous unrealized loss position, Fair Value 1,353,531 1,369,390
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss (119,598) (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 469,023 63,311
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss (4,398) (120)
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value 1,830,608 1,996,200
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss (255,088) (252,955)
Available-for-sale securities, continuous unrealized loss position, Fair Value 2,299,631 2,059,511
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss (259,486) (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 408,317 188,241
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss (3,539) (599)
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value 146,429 152,452
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss (2,664) (2,531)
Available-for-sale securities, continuous unrealized loss position, Fair Value 554,746 340,693
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss (6,203) (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 14,897 4,987
Available-for-sale securities, continuous unrealized loss position Less than 12 Months, Unrealized Loss (41) (1)
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Fair Value 53,111 63,382
Available-for-sale securities, continuous unrealized loss position 12 Months or Longer, Unrealized Loss (3,268) (3,134)
Available-for-sale securities, continuous unrealized loss position, Fair Value 68,008 68,369
Available-for-sale securities, continuous unrealized loss position, Unrealized Loss $ (3,309) $ (3,135)