Investments - Schedule of Amortized Cost, Gross Unrealized Gains and Losses, and Fair Value of Debt Securities Available-for-Sale (Detail) - USD ($) $ in Thousands	Dec. 31, 2023		Dec. 31, 2022
Schedule of Available-for-sale Securities [Line Items]
Debt Securities Available-for-sale, Cost or Adjusted /Amortized Cost	$ 606,646		$ 705,548
Debt Securities Available-for-sale, Gross Unrealized Gains	996		115
Debt Securities Available-for-sale, Gross Unrealized Losses	46,960		70,091
Debt Securities Available-for-sale, Fair Value	560,682		635,572
U.S. government and agency securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Debt Securities Available-for-sale, Cost or Adjusted /Amortized Cost	82,376	[1]	121,811	[2]
Debt Securities Available-for-sale, Gross Unrealized Gains	417	[1]	24	[2]
Debt Securities Available-for-sale, Gross Unrealized Losses	1,353	[1]	4,093	[2]
Debt Securities Available-for-sale, Fair Value	81,440	[1]	117,742	[2]
States, Municipalities and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Debt Securities Available-for-sale, Cost or Adjusted /Amortized Cost	92,739		104,361
Debt Securities Available-for-sale, Gross Unrealized Gains	12		0
Debt Securities Available-for-sale, Gross Unrealized Losses	8,958		12,734
Debt Securities Available-for-sale, Fair Value	83,793		91,627
Special Revenue [Member]
Schedule of Available-for-sale Securities [Line Items]
Debt Securities Available-for-sale, Cost or Adjusted /Amortized Cost	250,891		284,946
Debt Securities Available-for-sale, Gross Unrealized Gains	92		1
Debt Securities Available-for-sale, Gross Unrealized Losses	24,660		34,817
Debt Securities Available-for-sale, Fair Value	226,323		250,130
Corporate And Miscellaneous [Member]
Schedule of Available-for-sale Securities [Line Items]
Debt Securities Available-for-sale, Cost or Adjusted /Amortized Cost	180,640		194,430
Debt Securities Available-for-sale, Gross Unrealized Gains	475		90
Debt Securities Available-for-sale, Gross Unrealized Losses	11,989		18,447
Debt Securities Available-for-sale, Fair Value	$ 169,126		$ 176,073

[1] Includes securities at December 31, 2023 with a carrying amount of $26.3 million that were pledged as collateral for the advance agreement entered into with a financial institution in 2018. The Company is permitted to withdraw or exchange any portion of the pledged collateral over the minimum requirement at any time. The Company evaluated the available for sale investments that were in an unrealized loss position at December 31, 2023 and determined that the decline in fair value was caused by rising interest rates, resulting in no credit loss allowance recorded for the year ended December 31, 2023.

[2] Includes securities at December 31, 2022 with a carrying amount of $24.3 million that were pledged as collateral for the advance agreement entered into with a financial institution in 2018. The Company is permitted to withdraw or exchange any portion of the pledged collateral over the minimum requirement at any time.