Summary of Financial Instruments for Which Fair Value Option Has Been Elected (Detail) - USD ($) $ in Thousands	Mar. 31, 2026	Dec. 31, 2025
Fair Value, Option, Quantitative Disclosures [Line Items]
Loans and Receivables	$ 425,981	$ 205,158
Assets	6,157,534	5,093,618
Liabilities	2,038	181
Debt Securities
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments	3,901	7,553
Equity and Preferred Securities
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments	5,727,652	4,880,907
Corporate Treasury Commitments
Fair Value, Option, Quantitative Disclosures [Line Items]
Liabilities	$ 2,038	$ 181

Fair value of financial obligations, including, but not limited to, debt instruments, derivative liabilities, federal funds purchased and sold under agreements to repurchase, securities loaned or sold under agreements to repurchase, financial instruments sold not yet purchased, guarantees, line of credit, loans and notes payable, servicing liability, and trading liabilities.

- Definition

Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

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