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Fair Values of Assets and Liabilities - Additional Information (Detail) - USD ($) | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |  |
Random sample percentage of securities for each quarter | 100.00% |  |
Total gains or losses included in earnings | $ (4,329,000) | $ (589,000) |
Interest rate swaps transferred into Level 3 from Level 2 | 0 | 536,000 |
Corporate securities transferred from Level 3 to Level 2 | 0 | 536,000 |
Impaired loans considered to be credit risk of non-collection | 100,000 |  |
Updated appraisal requirement floor | 250,000 |  |
Other real estate owned | 2,765,000 | 6,805,000 |
Financial instrument of credit risk | 198,000 | 200,000 |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings On Assets Held At Year End | 0 | 0 |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Between Levels 1 And 2 | 0 | 0 |
Provision for credit losses | 5,087,000 | 18,480,000 | $ 14,948,000
Pooled Trust Preferred Collateralized Debt Obligations [Member] |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |  |
Total gains or losses included in earnings | (4,329,000) | (589,000) |
Interest rate swaps transferred into Level 3 from Level 2 | 0 | 0 |
Corporate securities transferred from Level 3 to Level 2 | 0 | 0 |
Other Assets [Member] |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |  |
Total gains or losses included in earnings | 0 | 0 |
Interest rate swaps transferred into Level 3 from Level 2 | 0 |  |
Corporate securities transferred from Level 3 to Level 2 | $ 0 | $ 0 |

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- Definition Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings On Assets Held At Year End + References No definition available. + Details
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- Definition Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Between Levels 1 And 2 + References No definition available. + Details
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- Definition Impaired loans fair value non collection. + References No definition available. + Details
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- Definition Percentage Of Securities Priced For Each Quarter + References No definition available. + Details
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- Definition Updated appraisal requirement floor. + References No definition available. + Details
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- Definition This item represents disclosure of all significant concentrations of credit risk or market risk arising from the subject financial instrument (as defined), whether from an individual counterparty or groups of counterparties. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(25)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(19)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(17)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
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- Definition Amount of transfer of financial instrument classified as an asset into level 3 of the fair value hierarchy. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(3) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
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- Definition Carrying amount as of the balance sheet date of land and buildings obtained through foreclosure proceedings or defeasance in full or partial satisfaction of a debt arrangement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 10 -Section S99 -Paragraph 6 -Subparagraph (SX 210.5-04(c)(Schedule III)) -URI http://asc.fasb.org/extlink&oid=27047687&loc=d3e5864-122674 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5162-111524 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 45 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=82891408&loc=d3e4437-111522 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 970 -SubTopic 360 -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-28) -URI http://asc.fasb.org/extlink&oid=6590653&loc=d3e638233-123024 + Details
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