Securities - Available for Sale Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Total securities available for sale	$ 340,273	$ 342,192
Gross Unrealized Gains	25,791	16,476
Gross Unrealized Losses	(190)	(169)
Fair Value	365,874	358,499
U.S. Treasury Securities and Obligations of U.S. Government Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Total securities available for sale	19,083	19,401
Gross Unrealized Gains	304	204
Gross Unrealized Losses	(1)	(4)
Fair Value	19,386	19,601
Obligations of States and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Total securities available for sale	207,077	193,646
Gross Unrealized Gains	19,170	12,409
Gross Unrealized Losses	(149)	(21)
Fair Value	226,098	206,034
Mortgage-backed Securities in Government Sponsored Entities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Total securities available for sale	114,113	129,145
Gross Unrealized Gains	6,317	3,863
Gross Unrealized Losses	(40)	(144)
Fair Value	$ 120,390	$ 132,864

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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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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