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Fair Value Measurements - Quantitative and Qualitative Information (Details)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Quantitative information about Level 3 fair value measurements
Mortgage servicing rights, fair value	$ 4,224,000	$ 5,935,000
Securities available-for-sale, at fair value	496,178,000	484,648,000
Fair Value, Inputs, Level 3 [Member]
Quantitative information about Level 3 fair value measurements
Securities available-for-sale, at fair value	4,319,000	5,419,000
US States and Political Subdivisions Debt Securities [Member]
Quantitative information about Level 3 fair value measurements
Securities available-for-sale, at fair value	249,259,000	249,175,000
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Quantitative information about Level 3 fair value measurements
Securities available-for-sale, at fair value	4,300,000	5,400,000
Collateralized Mortgage Obligations [Member]
Quantitative information about Level 3 fair value measurements
Securities available-for-sale, at fair value	56,585,000	57,984,000
Recurring
Quantitative information about Level 3 fair value measurements
Mortgage servicing rights, fair value	4,224,000	5,935,000
Recurring | Fair Value, Inputs, Level 3 [Member]
Quantitative information about Level 3 fair value measurements
Mortgage servicing rights, fair value	4,224,000	5,935,000
Recurring | US States and Political Subdivisions Debt Securities [Member]
Quantitative information about Level 3 fair value measurements
Securities available-for-sale, at fair value	249,259,000	249,175,000
Recurring | US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Quantitative information about Level 3 fair value measurements
Securities available-for-sale, at fair value	4,319,000	5,419,000
Recurring | Collateralized Mortgage Obligations [Member]
Quantitative information about Level 3 fair value measurements
Securities available-for-sale, at fair value	56,585,000	57,984,000
Recurring | Measurement Input, Discount Rate | Mortgage Servicing Rights [Member] | Discounted Cash Flow | Fair Value, Inputs, Level 3 [Member]
Quantitative information about Level 3 fair value measurements
Mortgage servicing rights, fair value	$ 4,224,000	$ 5,935,000
Recurring | Measurement Input, Discount Rate | Mortgage Servicing Rights [Member] | Discounted Cash Flow | Fair Value, Inputs, Level 3 [Member] | Minimum [Member]
Quantitative information about Level 3 fair value measurements
Servicing Asset, Measurement Input	11.0	10.0
Recurring | Measurement Input, Discount Rate | Mortgage Servicing Rights [Member] | Discounted Cash Flow | Fair Value, Inputs, Level 3 [Member] | Maximum [Member]
Quantitative information about Level 3 fair value measurements
Servicing Asset, Measurement Input	15.0	58.8
Recurring | Measurement Input, Discount Rate | Mortgage Servicing Rights [Member] | Discounted Cash Flow | Fair Value, Inputs, Level 3 [Member] | Weighted Average [Member]
Quantitative information about Level 3 fair value measurements
Servicing Asset, Measurement Input	11.0	10.1
Recurring | Measurement Input, Constant Prepayment Rate | Mortgage Servicing Rights [Member] | Discounted Cash Flow | Fair Value, Inputs, Level 3 [Member] | Minimum [Member]
Quantitative information about Level 3 fair value measurements
Servicing Asset, Measurement Input	5.5	0.0
Recurring | Measurement Input, Constant Prepayment Rate | Mortgage Servicing Rights [Member] | Discounted Cash Flow | Fair Value, Inputs, Level 3 [Member] | Maximum [Member]
Quantitative information about Level 3 fair value measurements
Servicing Asset, Measurement Input	59.1	69.0
Recurring | Measurement Input, Constant Prepayment Rate | Mortgage Servicing Rights [Member] | Discounted Cash Flow | Fair Value, Inputs, Level 3 [Member] | Weighted Average [Member]
Quantitative information about Level 3 fair value measurements
Servicing Asset, Measurement Input	19.5	14.1

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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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).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
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Fair value of an asset representing net future revenue from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
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Value of input used to measure servicing asset.

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-Topic 820
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