Loans Held for Investment and Allowance for Loan Losses - Additional Information (Detail)	3 Months Ended		6 Months Ended
	Jun. 30, 2022 USD ($) Restructuredloan	Jun. 30, 2021 USD ($) Restructuredloan	Jun. 30, 2022 USD ($) Restructuredloan	Jun. 30, 2021 USD ($) 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	$ 25,517,000	$ 30,114,000	$ 25,517,000	$ 30,114,000	$ 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
Commitments to lend additional funds to borrowers with loan that have been modified as TDRs	0		$ 0
Loans held by subsidiaries subject to blanket liens	3,690,957,000		3,690,957,000
Available line of credit	2,087,115,000		2,087,115,000
Line of credit	$ 0	$ 0	$ 0	$ 0	0
Troubled debt restructured loan | Restructuredloan	0	0	0	0
Unfunded loan commitments	$ 8,718,000	$ 6,751,000	$ 8,718,000	$ 6,751,000	6,436,000
Total Loans	5,878,582,000	5,304,602,000	5,878,582,000	5,304,602,000	$ 5,388,972,000
Provision for Loan and Lease Losses	4,103,000	(1,039,000)	7,850,000	(4,468,000)
Reversal of Provision for credit losses		1,039,000		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	1,247,000	167,000	2,282,000	1,265,000
Reversal of Provision for credit losses	$ 5,350,000	$ (1,206,000)	$ 10,132,000	$ (3,203,000)