v3.26.1
INVESTMENT SECURITIES - Amortized cost and estimated fair value of investment securities (Details) - USD ($)
$ in Thousands
 6 Months Ended 12 Months Ended
Jun. 30, 2026
Dec. 31, 2025
Available-for-Sale Portfolio:    
Amortized Cost $ 3,237,809 $ 3,148,728
Gross Unrealized Gains 644 526
Gross Unrealized Losses 280,490 273,913
Fair Value 2,957,963 2,875,341
Held-to-Maturity Portfolio:    
Amortized Cost 1,478,386 1,454,166
Gross Unrealized Gains 2,537 3,537
Gross Unrealized Losses 108,442 87,239
Fair Value 1,372,481 1,370,464
Other equity securities, at adjusted cost    
Equity securities, Fair values 3,700 4,400
Equity securities without readily determinable fair value amount 84,200 72,800
Government securities    
Available-for-Sale Portfolio:    
Amortized Cost 2,427,277 2,399,478
Gross Unrealized Gains 16 0
Gross Unrealized Losses 207,912 204,252
Fair Value 2,219,381 2,195,226
Held-to-Maturity Portfolio:    
Amortized Cost 1,183,312 1,168,487
Gross Unrealized Gains 0 0
Gross Unrealized Losses 107,538 87,003
Fair Value 1,075,774 1,081,484
Obligations of state and political subdivisions    
Available-for-Sale Portfolio:    
Amortized Cost 462,678 417,414
Gross Unrealized Gains 562 430
Gross Unrealized Losses 27,247 25,927
Fair Value 435,993 391,917
Government agency mortgage-backed securities    
Available-for-Sale Portfolio:    
Amortized Cost 329,485 322,253
Gross Unrealized Gains 53 96
Gross Unrealized Losses 45,087 43,464
Fair Value 284,451 278,885
Held-to-Maturity Portfolio:    
Amortized Cost 295,074 285,679
Gross Unrealized Gains 2,537 3,537
Gross Unrealized Losses 904 236
Fair Value 296,707 288,980
Corporate debt securities    
Available-for-Sale Portfolio:    
Amortized Cost 8,508 5,000
Gross Unrealized Gains 0 0
Gross Unrealized Losses 37 88
Fair Value 8,471 4,912
Government agency collateralized mortgage obligations    
Available-for-Sale Portfolio:    
Amortized Cost 9,861 4,583
Gross Unrealized Gains 13 0
Gross Unrealized Losses 207 182
Fair Value 9,667 4,401
Held-to-Maturity Portfolio:    
Amortized Cost 0  
Fair Value 0  
Federal Home Loan Bank Common Stock    
Other equity securities, at adjusted cost    
Equity securities without readily determinable fair value amount 40,400 33,200
Federal Reserve Bank Common Stock    
Other equity securities, at adjusted cost    
Equity securities without readily determinable fair value amount 33,300 33,300
Other Equity Securities    
Other equity securities, at adjusted cost    
Equity securities without readily determinable fair value amount   $ 6,300
Equity securities    
Other equity securities, at adjusted cost    
Equity securities without readily determinable fair value amount 5,300  
Other investment securities    
Other equity securities, at adjusted cost    
Equity securities without readily determinable fair value amount $ 5,200