v3.26.1
Securities - Additional Information (Details) - USD ($)
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Dec. 31, 2025
Debt Securities, Available-for-sale [Line Items]          
Debt securities, available-for-sale, allowance for credit loss, excluding accrued interest $ 0 $ 0 $ 0 $ 0 $ 0
Debt securities, available-for-sale, accrued interest, after allowance for credit loss 12,500,000   12,500,000   11,900,000
Debt securities, available-for-sale, accrued interest writeoff 0 0 0 0  
Debt securities, held-to-maturity, allowance for credit loss, excluding accrued interest 0 0 0 0 0
Debt securities, held-to-maturity, accrued interest, after allowance for credit loss 5,800,000   5,800,000   3,600,000
Debt securities, held-to-maturity, accrued interest, writeoff 0 $ 0 0 $ 0  
Federal Home Loan Bank of Boston          
Debt Securities, Available-for-sale [Line Items]          
Deposit liabilities, collateral issued, financial instruments 3,000,000,000.0   3,000,000,000.0   200,000,000
Other Purposes Required By Law          
Debt Securities, Available-for-sale [Line Items]          
Deposit liabilities, collateral issued, financial instruments 957,200,000   957,200,000   692,900,000
Federal Reserve Discount Window          
Debt Securities, Available-for-sale [Line Items]          
Deposit liabilities, collateral issued, financial instruments $ 387,200,000   $ 387,200,000   $ 414,200,000