Loans Held-for-Investment and Allowance for Credit Losses - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024	Dec. 31, 2024
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual, past due 90 days or more and still accruing, restructured loans and foreclosed assets	$ 63,708,000	$ 61,189,000	$ 63,708,000	$ 61,189,000	$ 63,096,000
Additional funds advanced in connection with impaired loans	0		0
Loans held by subsidiaries subject to blanket liens	5,637,716,000		5,637,716,000
Available line of credit	2,186,315,000		2,186,315,000
Undisbursed commitments	795,000,000		795,000,000
Reserve for unfunded commitments (Other liabilities)	9,914,000	7,433,000	9,914,000	7,433,000	$ 8,677,000
Provision for loan losses	2,432,000	5,910,000	5,423,000	7,166,000
Unfunded Loan Commitment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for loan losses	3,132,000	5,888,000	6,660,000	6,695,000
Reversal of Provision for credit losses	$ 700,000	$ 22,000	$ 1,237,000	$ 471,000