Borrowings and Subordinated Debentures - Narrative (Details) - USD ($)	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Prepayment Fees on Advances, Net	$ 6.6
Debt Weighted Average Interest Rate for Period	0.96%
Unused Lines of Credit
Debt Instrument [Line Items]
Amount outstanding	$ 0	$ 0	$ 0
Current borrowing capacity	180,000,000.0	180,000,000.0
Unused commitment fees		0
AFX short-term borrowings
Debt Instrument [Line Items]
Amount outstanding	50,000,000	50,000,000	300,000,000
Federal Reserve Bank Advances
Debt Instrument [Line Items]
Loans pledged as collateral	2,100,000,000	2,100,000,000
Amount outstanding	0	0	0
Federal Reserve Bank Advances \| FHLB secured advances
Debt Instrument [Line Items]
Borrowing capacity description	1,600,000,000	1,600,000,000
Federal Home Loan Bank of San Francisco
Debt Instrument [Line Items]
Loans pledged as collateral	5,600,000,000	5,600,000,000
Prepaid Term Borrowing Advances	750.0
Federal Home Loan Bank of San Francisco \| FHLB secured advances
Debt Instrument [Line Items]
Borrowing capacity description	3,600,000,000	3,600,000,000
Current outstanding	10,000,000	10,000,000	1,318,000,000
Federal Home Loan Bank of San Francisco \| FHLB unsecured overnight advance
Debt Instrument [Line Items]
Current outstanding	0	0	$ 141,000,000.0
Federal Home Loan Bank of San Francisco \| Unused Lines of Credit
Debt Instrument [Line Items]
Borrowing capacity description	$ 112,000,000.0	$ 112,000,000.0

Debt Weighted Average Interest Rate for Period

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- Definition

Prepaid Term Borrowing Advances

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Amount of commitment fees for the unused borrowing capacity under the long-term financing arrangement that is available to the entity.

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- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
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- Definition

Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

+ References

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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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- Definition

The carrying value as of the balance sheet date of the current portion of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
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-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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- Definition

Carrying amount as of the balance sheet date of loans that have been pledged as collateral for borrowings. If the secured party has the right by contract or custom to sell or re-pledge the collateral, then the debtor reclassifies that asset and report that asset in its statement of financial position separately from other assets not so encumbered.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 45
-Paragraph 1
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- Definition

Amount of income earned, after hedging basis adjustments, from fees charged for prepayment of certain Federal Home Loan Bank (FHLBank) advances before original maturity.

+ References

No definition available.

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