Securities - Additional Information (Detail) - USD ($)	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020
Schedule Of Securities [Line Items]
Debt securities available for sale, allowance for credit losses	$ 0	$ 0
Debt securities held to maturity, allowance for credit losses	50,000.00	40,000.00
Municipal bond portfolio, value	$ 1,000,000,000
Percentage of formal credit enhancement insurance of municipalities	61.00%
Available-for-sale debt securities
Schedule Of Securities [Line Items]
Accrued investment income receivable	$ 7,300,000	6,200,000
States of the U.S. and political subdivisions (municipals)
Schedule Of Securities [Line Items]
Debt securities held to maturity, allowance for credit losses	50,000.00	40,000.00
Held-to-maturity securities
Schedule Of Securities [Line Items]
Accrued investment income receivable	12,300,000	$ 12,500,000
Municipal Bonds \| Weighted Average
Schedule Of Securities [Line Items]
Average holding size of securities in bond portfolio	$ 3,600,000
Municipal Bonds \| Credit Concentration Risk \| General Obligation Bonds \| A Rating or Better \| Minimum
Schedule Of Securities [Line Items]
Percentage of portfolio	100.00%
Municipal Bonds \| Geographic Concentration Risk \| Pennsylvania, Ohio and Maryland
Schedule Of Securities [Line Items]
Percentage of portfolio	63.00%

The average holding size, aggregate value, of the securities in the municipal bond portfolio.

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The percentage as of the balance sheet date of municipal bonds that have formal credit enhancement insurance.

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Schedule Of Securities [Line Items]

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Interest, dividends, rents, ancillary and other revenues earned but not yet received by the entity on its investments.

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For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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Amount excluding accrued interest, of allowance for credit 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, excluding accrued interest, of allowance for credit loss on investment in debt security measured at amortized cost (held-to-maturity).

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Bonds or similar securities issued by state, city, or local governments or the agencies operated by state, city, or local governments 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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