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Fair Value of Assets and Liabilities - Summary of Valuation Techniques and Significant Unobservable Inputs Used in Non-Recurring Level 3 Fair Value Measurements of Assets and Liabilities (Detail)	12 Months Ended
	Dec. 31, 2020 USD ($) $ / shares		Dec. 31, 2019 USD ($) $ / shares		Dec. 31, 2018 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Principal portion of loans serviced, fair value	$ 107,131,000		$ 113,581,000
Loan collateral in process of foreclosure	$ 54,560,000	[1]	$ 52,711,000	[1]	$ 49,495,000
Equity Investments [Member] | Precedent Market Transactions [Member] | Equity Method Offering Price [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Equity Value | $ / shares	$ 8.73		$ 8.73
Equity Investments [Member] | Precedent Arms Length Offer [Member] | Financial Condition and Operating Performance Enterprise Value [Member] | Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Equity Value			$ 4,855,000
Equity Value			1.59
Equity Investments [Member] | Precedent Arms Length Offer [Member] | Financial Condition and Operating Performance Enterprise Value [Member] | Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Equity Value			$ 6,120,000
Equity Investments [Member] | Precedent Arms Length Offer [Member] | Discount Rate [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Equity Value			0.25
Impaired Loans [Member] | Market Approach [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Impaired loans, balance percentage	0.60
Impaired Loans [Member] | Market Approach [Member] | Historical and Actual Loss Experience [Member] | Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Impaired loans value	0.0150
Impaired Loans [Member] | Market Approach [Member] | Historical and Actual Loss Experience [Member] | Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Impaired loans value	0.0600
Impaired Loans [Member] | Market Approach [Member] | Measurement Input Median Transfer Price [Member] | Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Principal portion of loans serviced, fair value	$ 600
Impaired Loans [Member] | Market Approach [Member] | Measurement Input Median Transfer Price [Member] | Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Principal portion of loans serviced, fair value	108,700
Loan Collateral in Process of Foreclosure [Member] | Market Approach [Member] | Collateral Value [Member] | Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loan collateral in process of foreclosure value	700
Loan Collateral in Process of Foreclosure [Member] | Market Approach [Member] | Collateral Value [Member] | Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loan collateral in process of foreclosure value	32,300
Loan Collateral in Process of Foreclosure [Member] | Market Approach [Member] | Measurement Input Median Transfer Price [Member] | Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loan collateral in process of foreclosure value	600
Loan Collateral in Process of Foreclosure [Member] | Market Approach [Member] | Measurement Input Median Transfer Price [Member] | Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loan collateral in process of foreclosure value	108,700
Level 3 [Member] | Equity Investments [Member] | Investee Financial Analysis [Member] | Measurement Input Financial Condition and Operational Performance [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Equity investments	8,291,000		$ 7,435,000
Level 3 [Member] | Equity Investments [Member] | Precedent Market Transactions [Member] | Equity Method Offering Price [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Equity investments	1,455,000		1,455,000
Level 3 [Member] | Equity Investments [Member] | Investee Book Value Adjusted for Market Appreciation [Member] | Financial Condition and Operating Performance of the Investee [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Equity investments			$ 1,189,000
Level 3 [Member] | Impaired Loans [Member] | Market Approach [Member] | Historical and Actual Loss Experience [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Principal portion of loans serviced, fair value	62,174,000
Level 3 [Member] | Loan Collateral in Process of Foreclosure [Member] | Market Approach [Member] | Collateral Value [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loan collateral in process of foreclosure	1,432,000
Level 3 [Member] | Loan Collateral in Process of Foreclosure [Member] | Market Approach [Member] | Measurement Input Median Transfer Price [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loan collateral in process of foreclosure	$ 53,128,000
[1] Includes financed sales of this collateral to third parties that are reported separately from the loan portfolio, and that are conducted by Medallion Bank of $3,535 and $8,163 as of December 31, 2020 and 2019.

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