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Loans and Allowance for Credit Losses - Additional Information (Detail) | 12 Months Ended
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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 |

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- Definition Unfunded commitments related to nonperforming loans. + References No definition available. + Details
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- Definition Amount of gain (loss) recognized in the income statement for financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258 + Details
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- Definition The gains (losses) included in earnings that represent the difference between the sale price and the carrying value of loans and leases that were sold during the reporting period. This element refers to the gain (loss) and not to the cash proceeds of the sales. This element is a noncash adjustment to net income when calculating net cash generated by operating activities using the indirect method. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585 + Details
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