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Fair Values of Assets and Liabilities - Schedule of Assets Measured on Nonrecurring Basis (Detail) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total Assets | $ 779,966 | $ 829,181
Fair Value, Measurements, Nonrecurring [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Impaired loans | 38,494 | 38,669
Other Real Estate Owned Assets Fair Value | 3,264 | 7,566
Total Assets | 41,758 | 46,235
Level 1 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total Assets | 0 | 0
Level 1 [Member] | Fair Value, Measurements, Nonrecurring [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Impaired loans | 0 | 0
Other Real Estate Owned Assets Fair Value | 0 | 0
Total Assets | 0 | 0
Fair Value, Inputs, Level 2 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total Assets | 752,507 | 793,289
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Nonrecurring [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Impaired loans | 23,249 | 18,679
Other Real Estate Owned Assets Fair Value | 3,264 | 7,566
Total Assets | 26,513 | 26,245
Level 3 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total Assets | 27,459 | 35,892
Level 3 [Member] | Fair Value, Measurements, Nonrecurring [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Impaired loans | 15,245 | 19,990
Other Real Estate Owned Assets Fair Value | 0 | 0
Total Assets | 15,245 | 19,990
Total Gains (Losses) [Member] | Fair Value, Measurements, Nonrecurring [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair Value Measurement Of Assets On Nonrecurring Basis Net Losses On Impaired Loans | (1,548) | (9,032)
Fair Value Measurement Of Assets On Nonrecurring Basis Net Losses On Other Real Estate Owned | (1,099) | (703)
Fair Value Measurement Of Assets On Nonrecurring Basis Net Loss | $ (2,647) | $ (9,735)

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- Definition Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. + 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 (a) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
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