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Fair Values of Assets and Liabilities - Schedule of Assets Measured on Non-Recurring Basis (Detail) - USD ($) $ in Thousands | Sep. 30, 2018 | Dec. 31, 2017
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Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total Assets | $ 933,939 | $ 779,966
Fair Value, Measurements, Nonrecurring [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Impaired loans | 34,486 | 38,494
Other real estate owned | 4,164 | 3,264
Total Assets | 38,650 | 41,758
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 | 0 | 0
Total Assets | 0 | 0
Level 2 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total Assets | 929,748 | 752,507
Level 2 [Member] | Fair Value, Measurements, Nonrecurring [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Impaired loans | 14,940 | 23,249
Other real estate owned | 4,164 | 3,264
Total Assets | 19,104 | 26,513
Level 3 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total Assets | 4,191 | 27,459
Level 3 [Member] | Fair Value, Measurements, Nonrecurring [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Impaired loans | 19,546 | 15,245
Other real estate owned | 0 | 0
Total Assets | $ 19,546 | $ 15,245

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