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Disclosures about Fair Value of Assets and Liabilities - Quantitative Information about Unobservable Inputs Used in Recurring and Nonrecurring Level 3 Fair Value Measurements (Detail) $ in Thousands	3 Months Ended
	Jun. 30, 2019 USD ($)	May 31, 2020	Mar. 31, 2020 USD ($)	Dec. 31, 2019
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Mortgage servicing rights	$ 853		$ 821
Impaired loans (collateral-dependent)	33
Foreclosed assets	$ 512
Minimum [Member] | Discount Rate [Member] | Discounted Cash Flow [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Mortgage servicing rights, measurement input	950
Minimum [Member] | Constant Prepayment Rate [Member] | Market Comparable Properties [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Impaired loans (collateral-dependent)	8.3
Minimum [Member] | Marketability Discount [Member] | Discounted Cash Flow [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Mortgage servicing rights, measurement input			9.5
Minimum [Member] | Marketability Discount [Member] | Market Comparable Properties [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Impaired loans (collateral-dependent)	1,110		1,200
Minimum [Member] | Comparability Adjustments [Member] | Market Comparable Properties [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Foreclosed assets	780		5	0.05
Maximum [Member] | Discount Rate [Member] | Discounted Cash Flow [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Mortgage servicing rights, measurement input	1,150
Maximum [Member] | Constant Prepayment Rate [Member] | Market Comparable Properties [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Impaired loans (collateral-dependent)	11.0
Maximum [Member] | Marketability Discount [Member] | Discounted Cash Flow [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Mortgage servicing rights, measurement input			11.5
Maximum [Member] | Marketability Discount [Member] | Market Comparable Properties [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Impaired loans (collateral-dependent)	(1,110)	14.5
Maximum [Member] | Comparability Adjustments [Member] | Market Comparable Properties [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Foreclosed assets	(780)		0.12	0.12
Weighted Average [Member] | Discount Rate [Member] | Discounted Cash Flow [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Mortgage servicing rights, measurement input	(950)
Weighted Average [Member] | Constant Prepayment Rate [Member] | Market Comparable Properties [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Impaired loans (collateral-dependent)	9.0
Weighted Average [Member] | Marketability Discount [Member] | Discounted Cash Flow [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Mortgage servicing rights, measurement input			9.5
Weighted Average [Member] | Marketability Discount [Member] | Market Comparable Properties [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Impaired loans (collateral-dependent)			1,210
Weighted Average [Member] | Comparability Adjustments [Member] | Market Comparable Properties [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Foreclosed assets			11	0.11

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- Definition

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