Borrowings and Subordinated Debentures - Summary of Borrowings and Debentures (Details) - USD ($) $ in Thousands	9 Months Ended
Sep. 30, 2023	Dec. 31, 2022
Debt Instrument [Line Items]
Borrowings (including $123,782 at fair value)	$ 6,294,525	$ 1,764,030
Rate	5.43%	5.36%
Assets Sold under Agreements to Repurchase, Interest Rate	8.50%	0.00%
Assets Sold under Agreements to Repurchase, Carrying Amount	$ 1,260,743	$ 0
Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net	(10,900)
Business Exit Costs	4,800
AFX short-term borrowings
Debt Instrument [Line Items]
Line of Credit, Current		250,000
Balance	$ 0	$ 250,000
Rate	0.00%	4.68%
Credit-Link Notes
Debt Instrument [Line Items]
Long-term Debt, Percentage Bearing Variable Interest, Percentage Rate	16.00%	14.56%
Other Borrowings	$ 123,782	$ 132,030
Federal Home Loan Bank of San Francisco \| Secured Debt [Member]
Debt Instrument [Line Items]
Line of Credit, Current	$ 0	$ 1,270,000
Rate	0.00%	4.62%
Federal Home Loan Bank of San Francisco \| Secured Debt [Member] \| Bank Term Funding Program
Debt Instrument [Line Items]
Line of Credit, Current	$ 4,910,000	$ 0
Rate	4.38%	0.00%
Federal Home Loan Bank of San Francisco \| FHLB unsecured overnight advance
Debt Instrument [Line Items]
Line of Credit, Current	$ 0	$ 112,000
Rate	0.00%	4.37%

Carrying amount of assets sold under agreements to repurchase when the carrying amount (or market value, if higher than the carrying amount) of securities or other assets sold under repurchase agreements exceeds 10 percent of total assets.

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Interest rate on the amount to be repaid to the counterparty to the repurchase agreement when the carrying amount (or market value, if higher than the carrying amount) of securities or other assets sold under the repurchase agreement exceeds 10 percent of total assets.

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Amount of expenses associated with exit or disposal activities pursuant to an authorized plan. Includes, but is not limited to, one-time termination benefits, termination of an operating lease or other contract, consolidating or closing facilities, and relocating employees, and termination benefits associated with an ongoing benefit arrangement. Excludes expenses associated with special or contractual termination benefits, a discontinued operation or an asset retirement obligation.

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Amount of unamortized debt discount (premium) and debt issuance costs.

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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.

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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.

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Amount, after deduction of unamortized premium (discount) and debt issuance cost, of long-term debt. Excludes lease obligation.

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