Investment in community development loans mortgage backed securities small business loans.

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Investment Securities - Additional Information (Detail) - USD ($)	1 Months Ended	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Investment Holdings [Line Items]
Proceeds from sale of debt securities, available-for-sale			$ 0
Recoveries		$ 2,860,000	0
Securities, carrying value		1,660,000,000		$ 1,570,000,000
Charge-offs		0	6,640,000
Equity securities, at fair value		17,646,000		$ 17,697,000
Proceeds from sales of equity securities		0	0
(Loss) gain on equity securities		$ (129,000)	148,000
Redemption of funds, notice period		60 days
Unfunded commitments		$ 0
Investment in government guaranteed loans, mortgage-backed securities, small business loans		9,800,000
Signature Bank
Investment Holdings [Line Items]
Charge-offs	$ 6,600,000		$ 6,600,000
Community reinvestment funds
Investment Holdings [Line Items]
Equity securities, at fair value		7,800,000
Other financial institutions
Investment Holdings [Line Items]
Unfunded commitments		$ 0