v3.26.3
Investment Securities - Summary of Amortized Cost and Fair Value of Debt Securities by Contractual Maturity (Detail) - USD ($)
$ in Thousands
Sep. 30, 2026
Dec. 31, 2025
Investments, Debt and Equity Securities [Abstract]    
Due in one year or less, Amortized Cost, Available-for-sale $ 51,593  
Due in one year or less, Fair Value, Available-for-sale 51,424  
Due after one year through five years, Amortized Cost, Available-for-sale 98,047  
Due after one year through five years, Fair Value, Available-for-sale 106,749  
Due after five years through ten years, Amortized Cost, Available-for-sale 1,713,645  
Due after five years through ten years, Fair Value, Available-for-sale 1,457,665  
Due after ten years, Amortized Cost, Available-for-sale 2,079,935  
Due after ten years, Fair Value, Available-for-sale 1,911,995  
Amortized Cost, Available-for-sale 3,943,220 $ 2,982,228
Total Available-for-sale Securities, Debt Maturities, Available-for-sale, Fair Value 3,527,833 $ 2,683,070
Due in one year or less, Amortized Cost, Held-to-maturity 3,256  
Due after one year through five years, Amortized Cost, Held-to-maturity 133,396  
Due after five years through ten years, Amortized Cost, Held-to-maturity 525,373  
Due after ten years, Amortized Cost, Held-to-maturity 1,533,267  
Total Held-to-maturity, Debt Maturities, Amortized Cost Basis 2,195,292  
Due in one year or less, Fair Value, Held-to-maturity 3,240  
Due after one year through five years, Fair Value, Held-to-maturity 121,128  
Due after five years through ten years, Fair Value, Held-to-maturity 422,906  
Due after ten years, Fair Value, Held-to-maturity 1,187,210  
Total, Held-to-maturity, Fair Value $ 1,734,484