Investments - Gross Unrealized Gains and Losses and Cost or Amortized Cost and Fair Value of Investments Classified as Available-for-Sale (Detail) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale, Amortized Cost	$ 342,784	$ 324,597
Available-for-sale, Gross Unrealized Gains	5,338	17,829
Available-for-sale, Gross Unrealized Losses	(5,150)	(657)
Available-for-sale, Fair Value	342,972	341,769
Available-for-sale, Allowance for Credit Losses	0	0
States and Political Subdivisions [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale, Amortized Cost	200,313	202,008
Available-for-sale, Gross Unrealized Gains	4,541	14,538
Available-for-sale, Gross Unrealized Losses	(2,618)	(240)
Available-for-sale, Fair Value	202,236	216,306
Corporate Bonds [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale, Amortized Cost	114,642	93,947
Available-for-sale, Gross Unrealized Gains	780	2,751
Available-for-sale, Gross Unrealized Losses	(1,723)	(272)
Available-for-sale, Fair Value	113,699	96,426
U.S. Agency-Based Mortgage-Backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale, Amortized Cost	7,117	7,944
Available-for-sale, Gross Unrealized Gains		158
Available-for-sale, Gross Unrealized Losses	(155)	(13)
Available-for-sale, Fair Value	6,962	8,089
U.S. Treasury Securities and Obligations of U.S. Government Agencies [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale, Amortized Cost	20,712	20,698
Available-for-sale, Gross Unrealized Gains	17	382
Available-for-sale, Gross Unrealized Losses	(654)	(132)
Available-for-sale, Fair Value	$ 20,075	$ 20,948

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) 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, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) 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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Amortized cost 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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Amount 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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Amount 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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