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Investment Securities - Non-Marketable Securities Included in Other Assets (Details)	3 Months Ended		12 Months Ended
	Mar. 31, 2021 USD ($) $ / shares shares	Mar. 31, 2020 USD ($)	Dec. 31, 2020 USD ($) shares	Apr. 29, 2021
Schedule of Equity Method Investments [Line Items]
Federal home loan bank stock, par value (in usd per share) | $ / shares	$ 100
Investments in low income housing tax credit funds	$ 3,400,000		$ 3,500,000
Low income housing tax credits and other tax benefits	160,000
Low income housing amortization expense	135,000
Unfunded commitments for low income housing tax credit funds	$ 508,000
Subsequent event
Schedule of Equity Method Investments [Line Items]
Federal home loan bank, dividend rate percentage				6.00%
Visa Inc. Class B common stock
Schedule of Equity Method Investments [Line Items]
Number of shares of securities carried at cost (in shares) | shares	10,439		10,439
Carrying value of securities carried at cost	$ 0		$ 0
Fair value of Class B common stock	$ 3,600,000		$ 3,700,000
Visa Inc. | Visa Inc. Class B common stock
Schedule of Equity Method Investments [Line Items]
Conversion rate on common stock	1.6228		1.6228
Asset Derivatives
Schedule of Equity Method Investments [Line Items]
Federal home loan bank stock	$ 11,900,000		$ 11,900,000
Low-income housing tax credit investment
Schedule of Equity Method Investments [Line Items]
Impairment losses	$ 0	$ 0

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