Line items represent reporting concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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The amount by which the fair value of an investment is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Investment Securities - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Jan. 01, 2019	Dec. 31, 2018	Jan. 01, 2018
Investment [Line Items]
Proceeds from Sale of Available-for-sale Securities, Debt	$ 0
Other than temporary impairments		$ 0
Securities, carrying value	511,300,000			$ 476,300,000
Equity securities, at fair value	15,232,000			$ 15,921,000
Cumulative adjustment for adoption of ASU 2016-01			$ 125,000
Proceeds from sales of equity securities	1,138,000	0
Loss on equity securities	(353,000)	$ 18,000
Investment in government guaranteed loans, mortgage-backed securities, small business loans	9,800,000
Investment in community development loans	$ 3,500,000
Redemption of funds	60 days
Unfunded commitments	$ 0
Other financial institutions
Investment [Line Items]
Equity securities, at fair value	1,900,000
Community reinvestment funds
Investment [Line Items]
Equity securities, at fair value	$ 13,400,000
Retained Earnings
Investment [Line Items]
Cumulative adjustment for adoption of ASU 2016-01			$ 125,000		$ 2,043,000