Securities - Additional Information (Details) - USD ($)	3 Months Ended
Mar. 31, 2025	Mar. 31, 2024	Dec. 31, 2024
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, allowance for credit loss, excluding accrued interest	$ 0	$ 0	$ 0
Debt securities, available-for-sale, accrued interest, after allowance for credit loss	13,000,000.0		8,900,000
Debt securities, available-for-sale, accrued interest writeoff	0	0
Debt securities, held-to-maturity, allowance for credit loss, excluding accrued interest	0	0	0
Debt securities, held-to-maturity, accrued interest, after allowance for credit loss	900,000		900,000
Debt securities, held-to-maturity, accrued interest, writeoff	0	$ 0
Federal Home Loan Bank of Boston
Debt Securities, Available-for-sale [Line Items]
Deposit liabilities, collateral issued, financial instruments	300,000,000		1,000,000,000.0
Other Purposes Required By Law
Debt Securities, Available-for-sale [Line Items]
Deposit liabilities, collateral issued, financial instruments	576,600,000		687,900,000
Federal Reserve Discount Window
Debt Securities, Available-for-sale [Line Items]
Deposit liabilities, collateral issued, financial instruments	$ 440,500,000		$ 794,800,000

Amount, after allowance for credit loss, of accrued interest on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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