Fair Value of Financial Instruments - Summary of Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale debt securities, at fair value	$ 102,535	$ 91,791
Other investment securities:
Equity investment in mutual fund with readily determinable fair value	3,700	3,800
U.S. Government-sponsored agency securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale debt securities, at fair value		1,005
Residential mortgage-backed securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale debt securities, at fair value	27,214	19,704
Residential collateralized mortgage obligations
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale debt securities, at fair value	75,321	71,082
Fair Value, Measurements, Recurring
Other investment securities:
Equity investment in mutual fund with readily determinable fair value	3,734	3,773
Fair Value, Measurements, Recurring | U.S. Government-sponsored agency securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale debt securities, at fair value		1,005
Fair Value, Measurements, Recurring | Residential mortgage-backed securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale debt securities, at fair value	27,214	19,704
Fair Value, Measurements, Recurring | Residential collateralized mortgage obligations
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale debt securities, at fair value	75,321	71,082
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets (Level 1)
Other investment securities:
Equity investment in mutual fund with readily determinable fair value	3,734	3,773
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets (Level 1) | U.S. Government-sponsored agency securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale debt securities, at fair value		0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets (Level 1) | Residential mortgage-backed securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale debt securities, at fair value	0	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets (Level 1) | Residential collateralized mortgage obligations
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale debt securities, at fair value	0	0
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Other investment securities:
Equity investment in mutual fund with readily determinable fair value	0	0
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | U.S. Government-sponsored agency securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale debt securities, at fair value		1,005
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Residential mortgage-backed securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale debt securities, at fair value	27,214	19,704
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Residential collateralized mortgage obligations
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale debt securities, at fair value	75,321	71,082
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Other investment securities:
Equity investment in mutual fund with readily determinable fair value	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | U.S. Government-sponsored agency securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale debt securities, at fair value		0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Residential mortgage-backed securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale debt securities, at fair value	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Residential collateralized mortgage obligations
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale debt securities, at fair value	$ 0	$ 0