Fair Value of Assets and Liabilities - Summary of Valuation Techniques and Significant Unobservable Inputs Used in Recurring and Non-Recurring Level 3 Fair Value Measurements of Assets and Liabilities (Detail)	6 Months Ended		12 Months Ended
	Jun. 30, 2020 USD ($) $ / shares		Dec. 31, 2019 USD ($) $ / shares		Mar. 31, 2020 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Principal portion of loans serviced, fair value	$ 108,195,000		$ 113,581,000
Loan collateral in process of foreclosure	47,375,000	[1]	52,711,000	[1]	$ 46,817,000	$ 52,368,000	$ 49,808,000	$ 49,495,000
Level 3 [Member] | Equity Investments [Member] | Investee Financial Analysis [Member] | Measurement Input Financial Condition and Operational Performance [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity investments	8,934,000		7,435,000
Level 3 [Member] | Equity Investments [Member] | Precedent Market Transactions [Member] | Equity Method Offering Price [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity investments	$ 1,455,000		$ 1,455,000
Equity Value | $ / shares	$ 8.73		$ 8.73
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 Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity investments			$ 1,189,000
Level 3 [Member] | Equity Investments [Member] | Public Company Comparables [Member] | Discount Rate [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity Value			0.25
Level 3 [Member] | Equity Investments [Member] | Public Company Comparables [Member] | Financial Condition and Operating Performance Enterprise Value [Member] | Minimum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity Value			$ 4,855,000
Equity Value			1.59
Level 3 [Member] | Equity Investments [Member] | Public Company Comparables [Member] | Financial Condition and Operating Performance Enterprise Value [Member] | Maximum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity Value			$ 6,120,000
Equity Value			5.98
Level 3 [Member] | Impaired Loans [Member] | Market Approach [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impaired loans, balance percentage	0.60
Level 3 [Member] | Impaired Loans [Member] | Market Approach [Member] | Historical and Actual Loss Experience [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Principal portion of loans serviced, fair value	$ 44,557,000
Level 3 [Member] | Impaired Loans [Member] | Market Approach [Member] | Historical and Actual Loss Experience [Member] | Minimum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impaired loans value	0.0150
Level 3 [Member] | Impaired Loans [Member] | Market Approach [Member] | Historical and Actual Loss Experience [Member] | Maximum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impaired loans value	0.0600
Level 3 [Member] | Impaired Loans [Member] | Market Approach [Member] | Measurement Input Median Transfer Price [Member] | Minimum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Principal portion of loans serviced, fair value	$ 4,000
Level 3 [Member] | Impaired Loans [Member] | Market Approach [Member] | Measurement Input Median Transfer Price [Member] | Maximum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Principal portion of loans serviced, fair value	149,500
Level 3 [Member] | Impaired Loans [Member] | Discounted Cash Flow [Member] | Discount Rate [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Principal portion of loans serviced, fair value	$ 37,368,000
Impaired loans value	0.1278
Level 3 [Member] | Impaired Loans [Member] | Discounted Cash Flow [Member] | Measurement Input Terminal Value [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impaired loans value	$ 119,500
Level 3 [Member] | Impaired Loans [Member] | Discounted Cash Flow [Member] | Measurement Input Terms [Member] | Minimum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impaired loans value	0 months
Level 3 [Member] | Impaired Loans [Member] | Discounted Cash Flow [Member] | Measurement Input Terms [Member] | Maximum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impaired loans value	41 months
Level 3 [Member] | Impaired Loans [Member] | Discounted Cash Flow [Member] | Measurement Input Monthly Payments [Member] | Minimum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impaired loans value	$ 600
Level 3 [Member] | Impaired Loans [Member] | Discounted Cash Flow [Member] | Measurement Input Monthly Payments [Member] | Maximum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impaired loans value	5,000
Level 3 [Member] | Loan Collateral in Process of Foreclosure [Member] | Market Approach [Member] | Collateral Value [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Loan collateral in process of foreclosure	47,375,000
Level 3 [Member] | Loan Collateral in Process of Foreclosure [Member] | Market Approach [Member] | Measurement Input Median Transfer Price [Member] | Minimum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Loan collateral in process of foreclosure value	4,000
Level 3 [Member] | Loan Collateral in Process of Foreclosure [Member] | Market Approach [Member] | Measurement Input Median Transfer Price [Member] | Maximum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Loan collateral in process of foreclosure value	$ 149,500

[1] Includes financed sales of this collateral to third parties that are reported separately from the loan portfolio, and that are conducted by the Bank of $9,265 as of June 30, 2020 and $8,163 as of December 31, 2019.