Fair Value Measurements - Schedule of Balances of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Available-for-sale securities:
Available-for-sale securities	$ 87,853	$ 99,454	[1]
MSR assets	845	935	[1]
Fair Value, Measurements, Recurring
Available-for-sale securities:
Available-for-sale securities	87,853	99,454
MSR assets	845	935
Rabbi trust assets	959	1,082
Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring
Available-for-sale securities:
Available-for-sale securities		9,024
Rabbi trust assets	959	1,082
Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring
Available-for-sale securities:
Available-for-sale securities	82,180	87,780
Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring
Available-for-sale securities:
Available-for-sale securities	5,673	2,650
MSR assets	845	935
US Government Agencies and Mortgage Backed Securities
Available-for-sale securities:
Available-for-sale securities	48,870	67,597
US Government Agencies and Mortgage Backed Securities | Fair Value, Measurements, Recurring
Available-for-sale securities:
Available-for-sale securities	48,870	67,597
US Government Agencies and Mortgage Backed Securities | Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring
Available-for-sale securities:
Available-for-sale securities		7,024
US Government Agencies and Mortgage Backed Securities | Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring
Available-for-sale securities:
Available-for-sale securities	48,870	60,573
State and Municipal Obligations
Available-for-sale securities:
Available-for-sale securities	18,846	16,576
State and Municipal Obligations | Fair Value, Measurements, Recurring
Available-for-sale securities:
Available-for-sale securities	18,846	16,576
State and Municipal Obligations | Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring
Available-for-sale securities:
Available-for-sale securities	18,846	16,576
Corporate Bonds
Available-for-sale securities:
Available-for-sale securities	20,137	15,281
Corporate Bonds | Fair Value, Measurements, Recurring
Available-for-sale securities:
Available-for-sale securities	20,137	15,281
Corporate Bonds | Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring
Available-for-sale securities:
Available-for-sale securities		2,000
Corporate Bonds | Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring
Available-for-sale securities:
Available-for-sale securities	14,464	10,631
Corporate Bonds | Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring
Available-for-sale securities:
Available-for-sale securities	$ 5,673	$ 2,650

[1] Derived from audited December 31, 2019 Consolidated Financial Statements.