Loans and Allowance for Credit Losses - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2018 USD ($) Contract	Dec. 31, 2017 USD ($) Contract	Dec. 31, 2016 USD ($) Contract
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable Held-for-sale, Amount	$ 11,881,000	$ 14,850,000
Provision for credit losses	12,531,000	5,087,000	$ 18,480,000
Charge-offs	$ 15,113,000	$ 12,509,000
Number of loans modified | Contract	58	41	65
Total amount of loan modified	$ 8,829,000	$ 8,274,000	$ 10,275,000
Total gains or losses included in earnings	8,102,000	4,329,000
Loans with modification to rate and payment due to amortization	$ 300,000	300,000	$ 6,600,000
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	$ 1,600,000	2,400,000
Consumer Loan [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	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	$ 178,000