Investment Securities - Additional Information (Detail) - USD ($)	3 Months Ended			6 Months Ended
	Jun. 30, 2023	Mar. 31, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2022
Investment Holdings [Line Items]
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	$ 9,127,000		$ 19,836,000	$ 1,671,000	$ 50,936,000
Proceeds from sale of debt securities, available-for-sale	0		0	0	0
Securities, carrying value	1,630,000,000			1,630,000,000		$ 1,340,000,000
Equity securities, at fair value	17,429,000			17,429,000		$ 17,283,000
Proceeds from sales of equity securities	0		0	0	0
(Loss) gain on equity securities	(135,000)		(364,000)	$ 13,000	(849,000)
Redemption of funds, notice period				60 days
Unfunded commitments	0			$ 0
Investment in government guaranteed loans, mortgage-backed securities, small business loans	9,600,000			9,600,000
Charge-offs	0		0	6,640,000
(Benefit) provision for credit loss expense	(160,000)		1,535,000	6,330,000	2,719,000
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss, Writeoff	(148,000)		(369,000)	(287,000)	(8,173,000)
Signature Bank
Investment Holdings [Line Items]
Charge-offs		$ 6,600,000
(Benefit) provision for credit loss expense		$ 6,600,000
Financial Asset Acquired with Credit Deterioration
Investment Holdings [Line Items]
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss, Writeoff	0		0	0	(7,634,000)
Amortization of Gain on Debt Securities Reclassified to Held to Maturity
Investment Holdings [Line Items]
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	127,000		$ 148,000	253,000	$ 283,000
Community reinvestment funds
Investment Holdings [Line Items]
Equity securities, at fair value	7,800,000			7,800,000
Other financial institutions
Investment Holdings [Line Items]
Unfunded commitments	$ 0			$ 0