Loans and Allowance for Credit Losses - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2019 USD ($) Contract	Dec. 31, 2018 USD ($) Contract	Dec. 31, 2017 USD ($) Contract
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non Accrual Status Of Loans After Number Of Days Past Due	90 days
Loans Receivable Held-for-sale, Amount	$ 15,989,000	$ 11,881,000
Provision for credit losses	14,533,000	12,531,000	$ 5,087,000
Charge-offs	$ 12,300,000	$ 15,100,000
Number of loans modified | Contract	38	58	41
Total amount of loan modified	$ 1,928,000	$ 8,829,000	$ 8,274,000
Total gains or losses included in earnings	198,000	8,102,000
Loans with modification to rate and payment due to amortization	$ 800,000	300,000	300,000
Minimum days required for conversion of trouble debt to be in default	90 days
Impaired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unfunded commitments related to nonperforming loans	$ 1,700,000	1,600,000
Loans To Individuals [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non Accrual Status Of Loans After Number Of Days Past Due	150 days
Nonaccrual Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable Held-for-sale, Amount	$ 0	0
Gain (loss) on sale of impaired loans	400,000	$ 1,800,000	$ 21,000
SEC Schedule, 12-09, Reserve, Off-balance Sheet Activity [Member] | Impaired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Off balance sheet reserve to nonperforming loans	$ 12,000