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Loans and Allowance for Credit Losses - Additional Information (Detail) - USD ($) | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2018 | Jun. 30, 2017 | Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Non Accrual Status Of Loans After Number Of Days Past Due |  |  | 90 days |  |
Default Status Of TDRs After Number Of Days Past Due |  |  | 90 days |  |
Unfunded commitments related to nonperforming loans | $ 1,600,000 |  | $ 1,600,000 |  | $ 2,400,000
Off balance sheet reserve to nonperforming loans | 100,000 |  | 100,000 |  | 200,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales | 12,289,000 | $ 0 | 12,289,000 | $ 0 |
Total gains or losses included in earnings | 5,262,000 | 0 | $ 8,102,000 | 0 |
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 |  |
Impaired Loans [Member] |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Loans with modifications to rate and payment due to reamortization | 0 | $ 100,000 | $ 100,000 | 200,000 |
Nonaccrual Commercial Loans [Member] |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Loans Held for sale, Amount | $ 0 |  | 0 |  | $ 0
Loans and Leases Receivable, Gain (Loss) on Sales, Net |  |  | $ 1,200,000 | $ 0 |

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- Definition Loans with modifications to rate and payment due to reamortization. + References No definition available. + Details
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- Definition Off balance sheet reserve to nonperforming loans. + References No definition available. + Details
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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 Amount of sale of 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)(2) -URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258 + Details
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- Definition Reflects the net positive or negative amount derived from subtracting from net proceeds of sale and the carrying amounts, net of allocated reserves, of financial assets transferred to third parties in transactions that qualify for sales treatment. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 20 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=109247956&loc=d3e107425-111719 + Details
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