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Securities - Narrative (Details)
 9 Months Ended 12 Months Ended
Sep. 30, 2024
USD ($)
security
Dec. 31, 2023
USD ($)
security
Jun. 30, 2024
USD ($)
Sep. 30, 2023
USD ($)
Jun. 30, 2023
USD ($)
Dec. 31, 2022
USD ($)
Schedule of Held-to-Maturity Securities [Line Items]            
Investment securities, carrying value $ 415,200,000          
Number of securities in unrealized loss positions | security 2,338 2,290        
Unrealized loss positions $ 2,200,000,000 $ 2,100,000,000        
Percentage of portfolio 89.70% 85.10%        
Allowance for credit losses for available for sale debt securities $ 0 $ 0        
Allowance for credit loss 158,000 157,000 $ 158,000 $ 159,000 $ 164,000 $ 257,000
Investment securities, held to maturity 1,888,537,000 1,945,795,000        
Accrued interest receivable on available for sale debt securities 13,800,000 14,700,000        
State and municipal            
Schedule of Held-to-Maturity Securities [Line Items]            
Investment securities, held to maturity 1,056,869,000 1,088,499,000        
State and municipal | Internally-Assigned Rating Methodology            
Schedule of Held-to-Maturity Securities [Line Items]            
Investment securities, held to maturity $ 132,500,000 $ 143,700,000