Amount of investment securities sold at a no gain or loss on sale.

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Gross Realized Investment Gains

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Investment Securities [Line Items]

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Life of mortgage backed securities.

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Percentage of aggregate depreciation in unrealized losses.

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Securities Pledged as Collateral

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Number of investment positions in available-for-sale investments in a continuous unrealized loss position for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement.

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-Publisher FASB
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Amount of unrealized and realized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of realized gain on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Amount of realized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of cash inflow from sale of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Debt securities issued by a United States government agency such as Government National Mortgage Association (Ginnie Mae), Federal Home Loan Mortgage Corporation (Freddie Mac), and Federal National Mortgage Association (Fannie Mae), which are short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

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Investment Securities - Additional Information (Detail)	12 Months Ended
Investment Securities - Additional Information (Detail)	Dec. 31, 2019 USD ($) Investmentsecurities	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Investment Securities [Line Items]
Proceeds from sales of debt securities	$ 127,066,000	$ 293,279,000	$ 25,757,000
Gross realized gains		207,000
Realized gain	338,000
Gain (loss) on available for sale security			961,000
Gross realized losses	(228,000)
Investment securities sold			$ 24,796,000
Securities pledged as collateral	466,321,000	$ 597,591,000
Residential real estate mortgage-backed securities	$ 827,924,000
Life of mortgage-backed securities	4 years 10 months 24 days
Obligations of U.S. government agencies
Investment Securities [Line Items]
Available for sale securities in unrealized loss position \| Investmentsecurities	16
Percentage of aggregate depreciation in unrealized losses	0.63%
Obligations of states and political subdivisions
Investment Securities [Line Items]
Available for sale securities in unrealized loss position \| Investmentsecurities	1
Percentage of aggregate depreciation in unrealized losses	0.13%
Asset backed securities
Investment Securities [Line Items]
Available for sale securities in unrealized loss position \| Investmentsecurities	20
Percentage of aggregate depreciation in unrealized losses	2.01%