Loans Held for Investment and Allowance for Loan Losses - Additional Information (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2022 USD ($) Restructuredloan	Sep. 30, 2021 USD ($) Restructuredloan	Sep. 30, 2022 USD ($) Restructuredloan	Sep. 30, 2021 USD ($) Restructuredloan	Dec. 31, 2021 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual, past due 90 days or more and still accruing, restructured loans and foreclosed assets	$ 24,619,000	$ 25,283,000	$ 24,619,000	$ 25,283,000	$ 34,158,000
Additional funds advanced in connection with impaired loans	0		$ 0
Default for purposes of this disclosure is a troubled debt restructured loan			90 days
Loans held by subsidiaries subject to blanket liens	3,901,376,000		$ 3,901,376,000
Available line of credit	2,258,125,000		2,258,125,000
Line of credit	$ 0	$ 0	$ 0	$ 0	0
Troubled debt restructured loan | Restructuredloan	0	1	0	1
Reserve for unfunded commitments (Other liabilities)	$ 10,879,000	$ 6,751,000	$ 10,879,000	$ 6,751,000	6,436,000
Total Loans	6,255,488,000	$ 5,286,494,000	6,255,488,000	5,286,494,000	$ 5,388,972,000
Provision for Loan and Lease Losses	(1,060,000)		(8,910,000)	4,468,000
Reversal of Provision for credit losses				4,468,000
Federal Home Loan Bank Borrowings [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Line of credit	0		0
Unfunded Loan Commitment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for Loan and Lease Losses	2,161,000		4,443,000	1,265,000
Reversal of Provision for credit losses	$ 3,221,000		$ 13,353,000	$ 3,203,000