Borrowings and Subordinated Debt - Summary of Borrowings and Debentures (Details) - USD ($) $ in Thousands	Mar. 31, 2026	Dec. 31, 2025
Debt Instrument [Line Items]
Long-Term Debt, Percentage Bearing Fixed Interest, Percentage Rate	4.33%	4.47%
Other Short-Term Borrowings	$ 440,000	$ 240,000
Short-Term Debt, Other, Average Rate Paid	3.68%	3.69%
Total Borrowings	$ 2,551,250	$ 2,063,819
Borrowings (including $111,250 and $113,634 at fair value, respectively)	2,551,250	2,063,819
Credit-linked notes
Debt Instrument [Line Items]
Credit-linked Notes	$ 111,250	$ 113,634
Credit-linked ,Variable interest, percentage rate	14.41%	14.63%
Federal Home Loan Bank of San Francisco | Secured Debt
Debt Instrument [Line Items]
Line of credit, current	$ 2,000,000	$ 1,710,185
Long-Term Debt, Percentage Bearing Fixed Interest, Percentage Rate	3.91%	3.90%