Loans Held for Investment and Allowance for Loan Losses - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual, past due 90 days or more and still accruing, restructured loans and foreclosed assets	$ 61,189,000	$ 29,249,000	$ 61,189,000	$ 29,249,000	$ 35,096,000
Additional funds advanced in connection with impaired loans	0		0
Loans held by subsidiaries subject to blanket liens	5,136,239,000		5,136,239,000
Available line of credit	2,026,305,000		2,026,305,000
Undisbursed commitments	786,500,000		786,500,000
Reserve for unfunded commitments (Other liabilities)	7,433,000	9,448,000	7,433,000	9,448,000	$ 7,903,000
Provision for loan losses	5,910,000	6,522,000	7,166,000	11,229,000
Unfunded Loan Commitment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for loan losses	5,888,000	5,573,000	6,695,000	8,354,000
Reversal of Provision for credit losses	$ 22,000	$ 949,000	$ 471,000	$ 2,875,000