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Investment Securities - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Jan. 01, 2019	Dec. 31, 2018	Jan. 01, 2018
Investment [Line Items]
Proceeds from sales of available for sale securities			$ 0	$ 0
Other than temporary impairments		$ 0
Securities, carrying value	$ 576,200,000		576,200,000			$ 476,300,000
Equity securities, at fair value	15,552,000		15,552,000			$ 15,921,000
Cumulative adjustment for adoption of ASU 2016-01					$ 125,000
Proceeds from sales of equity securities			1,153,000	2,155,000
Loss on equity securities	(72,000)	$ 439,000	(525,000)	$ 384,000
Investment in community development loans	3,500,000		$ 3,500,000
Redemption of funds			60 days
Unfunded commitments	0		$ 0
Investment in government guaranteed loans, mortgage-backed securities, small business loans	10,200,000		10,200,000
Other financial institutions
Investment [Line Items]
Equity securities, at fair value	1,800,000		1,800,000
Community reinvestment funds
Investment [Line Items]
Equity securities, at fair value	$ 13,700,000		$ 13,700,000
Retained Earnings
Investment [Line Items]
Cumulative adjustment for adoption of ASU 2016-01					$ 125,000		$ 2,043,000