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Investment Securities - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Investment Holdings [Line Items]
Proceeds from sale of debt securities, available-for-sale	$ 0	$ 0	$ 0	$ 94,696,000
Debt securities, available-for-sale, realized gain	9,000			569,000
Debt securities, available-for-sale, realized loss				(227,000)
Securities, carrying value	653,300,000		653,300,000		$ 578,000,000.0
Equity securities, at fair value	15,440,000		15,440,000		$ 14,694,000
Proceeds from sales of equity securities			0	0
Loss on equity securities	(11,000)	$ (198,000)	$ 133,000	$ 455,000
Redemption of funds, notice period			60 days
Unfunded commitments	0		$ 0
Investment in government guaranteed loans, mortgage-backed securities, small business loans	11,900,000		11,900,000
Community reinvestment funds
Investment Holdings [Line Items]
Equity securities, at fair value	3,500,000		3,500,000
Other financial institutions
Investment Holdings [Line Items]
Unfunded commitments	$ 0		$ 0