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Investment Securities - Amortized Cost and Estimated Fair Value of Securities Contractual Maturity (Details) - USD ($)
$ in Thousands
Sep. 30, 2025
Dec. 31, 2024
Amortized Cost    
Due in one year or less, Amortized Cost $ 32,853  
Due in one year or less, Amortized Cost 0  
Due after one year through five years, Amortized Cost 257,956  
Due after one year through five years, Amortized Cost 104,620  
Due after five years through ten years, Amortized Cost 394,695  
Due after five years through ten years, Amortized Cost 364,055  
Due after ten years, Amortized Cost 773,232  
Due after ten years, Amortized Cost 678,868  
Amortized Cost 3,163,880 $ 3,410,272
Amortized Cost 1,266,205 1,277,209
Estimated Fair Value    
Due in one year or less, Estimated Fair Value 32,425  
Due in one year or less, Estimated Fair Value 0  
Due after one year through five years, Estimated Fair Value 247,955  
Due after one year through five years, Estimated Fair Value 101,940  
Due after five years through ten years, Estimated Fair Value 375,621  
Due after five years through ten years, Estimated Fair Value 338,975  
Due after ten years, Estimated Fair Value 708,505  
Due after ten years, Estimated Fair Value 600,559  
Total, Estimated Fair Value 2,924,496 3,072,639
Estimated Fair Value 1,157,119 1,142,940
U.S. government-sponsored mortgage-backed securities    
Amortized Cost    
Securities not due at a single maturity date, Amortized Cost 1,378,237  
Securities not due at a single maturity date, Amortized Cost 118,662  
Amortized Cost 1,378,237 1,527,463
Amortized Cost 118,662 124,169
Estimated Fair Value    
Securities not due at a single maturity date, Estimated Fair Value 1,241,056  
Securities not due at a single maturity date, Estimated Fair Value 115,645  
Total, Estimated Fair Value 1,241,056 1,324,684
Estimated Fair Value 115,645 117,474
Private mortgage-backed securities    
Amortized Cost    
Securities not due at a single maturity date, Amortized Cost 155,155  
Securities not due at a single maturity date, Amortized Cost 0  
Amortized Cost 155,155 184,643
Estimated Fair Value    
Securities not due at a single maturity date, Estimated Fair Value 147,901  
Securities not due at a single maturity date, Estimated Fair Value 0  
Total, Estimated Fair Value 147,901 171,394
Non-government-sponsored asset backed securities    
Amortized Cost    
Securities not due at a single maturity date, Amortized Cost 171,752  
Securities not due at a single maturity date, Amortized Cost 0  
Amortized Cost 171,752 228,751
Estimated Fair Value    
Securities not due at a single maturity date, Estimated Fair Value 171,033  
Securities not due at a single maturity date, Estimated Fair Value 0  
Total, Estimated Fair Value $ 171,033 $ 225,648