Investment Securities - Additional Information (Detail)	9 Months Ended
Sep. 30, 2021 USD ($) Securities	Sep. 30, 2020 USD ($) Securities	Dec. 31, 2020 Securities
Investments Debt And Equity Securities [Line Items]
Number of securities held in portfolio \| Securities	38		29
Number of available for sale securities in unrealized loss positions \| Securities	0	6
Net unrealized gains on available for sale investment securities	$ 315,000	$ 910,000
Payments to acquire securities	$ 36,500,000	35,400,000
Proceeds from sale of securities		$ 7,700,000

Investments debt and equity securities.

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Number of securities held in portfolio.

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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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Amount of unrealized 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 cash outflow to acquire 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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