Investment Securities - Additional Information (Detail)	3 Months Ended	6 Months Ended
Jun. 30, 2020 USD ($) numberOfContracts	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) numberOfContracts	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($) numberOfContracts
Investments
Loss upon acquisition of interest-only GNMA securities	$ 0	$ 7,476,000	$ 0	$ 7,476,000
Unrealized gain (loss) on investment securities	1,200,000	(300,000)	(200,000)	(300,000)
Proceeds from sales of investment securities available for sale	109,200,000		109,207,000	0
Realized gain	$ 4,400,000	0	$ 8,300,000	$ 0
Number of available-for-sale investment securities in the less than twelve month category \| numberOfContracts	1		1		0
Number of available-for-sale investment securities in the twelve month category \| numberOfContracts	0		0		0
Pledged investment securities fair value	$ 16,900,000		$ 16,900,000		$ 20,400,000
Interest-only GNMA securities
Investments
Loss upon acquisition of interest-only GNMA securities		$ 7,500,000
Interest-only GNMA securities	$ 14,396,000		$ 14,396,000		$ 16,272,000

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Number of investments in debt securities measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without an allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Number of investments in debt securities measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without an allowance for credit loss. Includes beneficial interest in securitized financial asset.

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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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Amount of unrealized gain (loss) on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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Amount of investments classified as other.

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Sum of the carrying amounts as of the date of the latest financial statement presented of securities which are owned but transferred to another party to serve as collateral to partially or fully secure a debt obligation, repurchase agreement or other current or potential obligation, and for which the transferee is not permitted to sell or re-pledge them to an unrelated party.

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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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