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Investment Securities - Summary of Amortized Cost and Estimated Fair Values of Available for Sale Securities (Detail) - USD ($)
$ in Thousands
Dec. 31, 2025
Dec. 31, 2024
Schedule of Investments [Line Items]    
Amortized Cost $ 3,264,860 $ 3,282,690
Gross Unrealized Gains 11,231 966
Gross Unrealized Losses 216,639 323,937
Allowance For Credit Losses 0 0
Estimated Fair Value 3,059,452 2,959,719
U.S. Treasury Securities and Obligations of U.S. Government Corporations and Agencies [Member]    
Schedule of Investments [Line Items]    
Amortized Cost 283,058 248,867
Gross Unrealized Gains 75 59
Gross Unrealized Losses 1,476 3,084
Allowance For Credit Losses 0 0
Estimated Fair Value 281,657 245,842
State and Political Subdivisions [Member]    
Schedule of Investments [Line Items]    
Amortized Cost 572,217 574,580
Gross Unrealized Gains 343 8
Gross Unrealized Losses 55,634 79,515
Allowance For Credit Losses 0 0
Estimated Fair Value 516,926 495,073
Residential mortgage-backed securities Agency [Member]    
Schedule of Investments [Line Items]    
Amortized Cost 1,467,436 1,226,400
Gross Unrealized Gains 5,517 433
Gross Unrealized Losses 114,317 167,114
Allowance For Credit Losses 0 0
Estimated Fair Value 1,358,636 1,059,719
Residential Mortgage-Backed Securities, Non-agency [Member]    
Schedule of Investments [Line Items]    
Amortized Cost 42,792 88,392
Gross Unrealized Gains 330 262
Gross Unrealized Losses 4,237 6,531
Allowance For Credit Losses 0 0
Estimated Fair Value 38,885 82,123
Commercial Mortgage-Backed Securities Agency [Member]    
Schedule of Investments [Line Items]    
Amortized Cost 416,177 372,646
Gross Unrealized Gains 4,948 38
Gross Unrealized Losses 26,052 42,698
Allowance For Credit Losses 0 0
Estimated Fair Value 395,073 329,986
Asset-backed Securities [Member]    
Schedule of Investments [Line Items]    
Amortized Cost 225,617 476,863
Gross Unrealized Gains 18 166
Gross Unrealized Losses 2,381 2,047
Allowance For Credit Losses 0 0
Estimated Fair Value 223,254 474,982
Single Issue Trust Preferred Securities [Member]    
Schedule of Investments [Line Items]    
Amortized Cost 13,319 13,296
Gross Unrealized Gains 0 0
Gross Unrealized Losses 661 1,377
Allowance For Credit Losses 0 0
Estimated Fair Value 12,658 11,919
Other Corporate Securities [Member]    
Schedule of Investments [Line Items]    
Amortized Cost 244,244 281,646
Gross Unrealized Gains 0 0
Gross Unrealized Losses 11,881 21,571
Allowance For Credit Losses 0 0
Estimated Fair Value $ 232,363 $ 260,075