Borrowings and Subordinated Debentures - Borrowing Type (Details) - USD ($)	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Debt Instrument [Line Items]
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate	5.06%	4.92%
Borrowings	$ 1,392,838,000	$ 2,915,416,000
Acquisition Discount on Senior Notes	(1,024,000)	(4,094,000)
Long-Term Debt	1,391,814,000	2,911,322,000
Other Borrowings, Fair Value Disclosure	118,838,000	123,116,000
Federal Reserve Bank Advances [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Amount Outstanding	$ 0	$ 0
Credit-Link Notes
Debt Instrument [Line Items]
Long-term Debt, Percentage Bearing Variable Interest, Percentage Rate	15.29%	16.02%
Long-term Debt, Percentage Bearing Variable Interest, Amount		$ 123,116,000
Other Borrowings, Fair Value Disclosure	$ 118,838,000	$ 123,116,000	$ 132,030,000	$ 0
American Financial Exchange
Debt Instrument [Line Items]
Line of Credit Facility, Amount Outstanding	$ 0
Five Point Two Five Percent Senior Notes Due April152025
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.25%	5.25%
Senior Notes	$ 174,000,000	$ 174,000,000
Federal Home Loan Bank of San Francisco | Secured Debt
Debt Instrument [Line Items]
Line of Credit, Current	$ 1,100,000,000	$ 0
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate	3.93%	0.00%
Federal Home Loan Bank of San Francisco | Secured Debt | Bank Term Funding Program
Debt Instrument [Line Items]
Line of Credit, Current	$ 0	$ 2,618,300,000
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate	0.00%	4.37%