Commitments and Contingencies - Narrative (Details) - USD ($)	9 Months Ended	12 Months Ended
Sep. 30, 2020	Dec. 31, 2019
Commitment And Contingencies
Loss reserve for unfunded loan commitments	$ 350,000	$ 350,000
Unused borrowing capacity		172,000,000
Maximum borrowings outstanding at any month-end		55,000,000
Short-term FHLB advances outstanding		30,000,000.0
FHLB advances—long-term		0
Federal Reserve Bank Of San Francisco
Commitment And Contingencies
Unused borrowing capacity	144,000,000	146,000,000
Federal Reserve Bank Of San Francisco \| Consumer loans
Commitment And Contingencies
Loans pledged as collateral to support FHLB and FRB borrowings	178,000,000	210,000,000
Federal Reserve Bank Of San Francisco \| Commercial loans
Commitment And Contingencies
Loans pledged as collateral to support FHLB and FRB borrowings	178,000,000	$ 210,000,000
Federal Home Loan Bank of San Francisco
Commitment And Contingencies
Loans pledged as collateral to support FHLB and FRB borrowings	443,000,000
Unused borrowing capacity	256,000,000
Maximum borrowings outstanding at any month-end	$ 74,000,000.0
FHLB Advances
Commitment And Contingencies
Weighted-average annualized interest rate	1.67%	1.82%
Letter of credit
Commitment And Contingencies
Commitment to fund certain loans including letter of credit	$ 336,000,000	$ 316,000,000

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Amount of unused borrowing capacity under the long-term financing arrangement that is available to the entity as of the balance sheet date.

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Weighted average interest rate of debt outstanding.

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The maximum balance outstanding at any month end during the period as of the Balance Sheet date.

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Amount of advance from Federal Home Loan Bank (FHLBank) maturing in next fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions.

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The noncurrent portion of Federal Home Loan Bank borrowings initially due beyond one year or beyond the normal operating cycle if longer.

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The fair value, as of the date of each statement of financial position presented, of loans which are owned but transferred to serve as collateral for the payment of the related debt obligation primarily arising from secured borrowings and repurchase agreements, and that are reclassified and separately reported in the statement of financial position because the transferee has the right by contract or custom to sell or re-pledge them.

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Amount of expense related to other loss.

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