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Investment Securities - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 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	$ 518,500,000		518,500,000			$ 476,300,000
Equity securities, at fair value	15,382,000		15,382,000			$ 15,921,000
Cumulative adjustment for adoption of ASU 2016-01					$ 125,000
Proceeds from sales of equity securities			1,153,000	1,734,000
Loss on equity securities	(100,000)	$ (73,000)	(453,000)	$ (55,000)
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	10,100,000		10,100,000
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	$ 13,600,000		$ 13,600,000
Retained Earnings
Investment [Line Items]
Cumulative adjustment for adoption of ASU 2016-01					$ 125,000		$ 2,043,000