v3.26.1
Investment Securities - Summary of Amortized Cost and Estimated Fair Values of Available for Sale Securities (Detail) - USD ($)
$ in Thousands
Jun. 30, 2026
Dec. 31, 2025
Schedule of Investments [Line Items]    
Amortized Cost $ 3,531,722 $ 3,264,860
Gross Unrealized Gains 6,517 11,231
Gross Unrealized Losses 218,489 216,639
Allowance For Credit Losses 0 0
Estimated Fair Value 3,319,750 3,059,452
U.S. Treasury Securities and Obligations of U.S. Government Corporations and Agencies [Member]    
Schedule of Investments [Line Items]    
Amortized Cost 281,141 283,058
Gross Unrealized Gains 48 75
Gross Unrealized Losses 1,398 1,476
Allowance For Credit Losses 0 0
Estimated Fair Value 279,791 281,657
State and Political Subdivisions [Member]    
Schedule of Investments [Line Items]    
Amortized Cost 564,691 572,217
Gross Unrealized Gains 431 343
Gross Unrealized Losses 55,882 55,634
Allowance For Credit Losses 0 0
Estimated Fair Value 509,240 516,926
Residential mortgage-backed securities Agency [Member]    
Schedule of Investments [Line Items]    
Amortized Cost 1,915,333 1,467,436
Gross Unrealized Gains 2,223 5,517
Gross Unrealized Losses 127,368 114,317
Allowance For Credit Losses 0 0
Estimated Fair Value 1,790,188 1,358,636
Residential Mortgage-Backed Securities, Non-agency [Member]    
Schedule of Investments [Line Items]    
Amortized Cost 41,938 42,792
Gross Unrealized Gains 470 330
Gross Unrealized Losses 4,060 4,237
Allowance For Credit Losses 0 0
Estimated Fair Value 38,348 38,885
Commercial Mortgage-Backed Securities Agency [Member]    
Schedule of Investments [Line Items]    
Amortized Cost 327,174 416,177
Gross Unrealized Gains 3,308 4,948
Gross Unrealized Losses 17,722 26,052
Allowance For Credit Losses 0 0
Estimated Fair Value 312,760 395,073
Asset-backed Securities [Member]    
Schedule of Investments [Line Items]    
Amortized Cost 175,611 225,617
Gross Unrealized Gains 37 18
Gross Unrealized Losses 2,121 2,381
Allowance For Credit Losses 0 0
Estimated Fair Value 173,527 223,254
Single Issue Trust Preferred Securities [Member]    
Schedule of Investments [Line Items]    
Amortized Cost 13,330 13,319
Gross Unrealized Gains 0 0
Gross Unrealized Losses 372 661
Allowance For Credit Losses 0 0
Estimated Fair Value 12,958 12,658
Other Corporate Securities [Member]    
Schedule of Investments [Line Items]    
Amortized Cost 212,504 244,244
Gross Unrealized Gains 0 0
Gross Unrealized Losses 9,566 11,881
Allowance For Credit Losses 0 0
Estimated Fair Value $ 202,938 $ 232,363