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Securities - Summary of Investments in an Unrealized Loss Position that were Temporarily Impaired (Detail) - USD ($) $ in Thousands | Dec. 31, 2017 | Dec. 31, 2016
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Securities available for sale: |  |
Less than 12 months - Fair value | $ 34,432 | $ 66,073
Less than 12 months - Unrealized (loss) | (339) | (1,429)
12 months or more - Fair value | 32,323 | 5,499
12 months or more - Unrealized (loss) | (1,153) | (208)
Fair Value | 66,755 | 71,572
Unrealized (Loss) | (1,492) | (1,637)
Securities held to maturity: |  |
Less than 12 months - Fair value | 25,190 | 48,980
Less than 12 months - Unrealized (loss) | (250) | (708)
12 months or more - Fair value | 13,297 | 0
12 months or more - Unrealized (loss) | (346) | 0
Fair Value | 38,487 | 48,980
Unrealized (Loss) | (596) | (708)
Total securities, Less than 12 months - Fair value | 59,622 | 115,053
Total securities, Less than 12 months - Unrealized (loss) | (589) | (2,137)
Total securities, 12 months or more - Fair value | 45,620 | 5,499
Total securities, 12 months or more - Unrealized (loss) | (1,499) | (208)
Total securities, Fair value | 105,242 | 120,552
Total securities, Unrealized (loss) | (2,088) | (2,345)
U.S. agency and mortgage-backed securities |  |
Securities available for sale: |  |
Less than 12 months - Fair value | 29,963 | 60,943
Less than 12 months - Unrealized (loss) | (286) | (1,249)
12 months or more - Fair value | 30,362 | 5,499
12 months or more - Unrealized (loss) | (1,051) | (208)
Fair Value | 60,325 | 66,442
Unrealized (Loss) | (1,337) | (1,457)
Securities held to maturity: |  |
Less than 12 months - Fair value | 18,301 | 34,770
Less than 12 months - Unrealized (loss) | (205) | (483)
12 months or more - Fair value | 13,297 | 0
12 months or more - Unrealized (loss) | (346) | 0
Fair Value | 31,598 | 34,770
Unrealized (Loss) | (551) | (483)
Obligations of states and political subdivisions |  |
Securities available for sale: |  |
Less than 12 months - Fair value | 4,469 | 5,130
Less than 12 months - Unrealized (loss) | (53) | (180)
12 months or more - Fair value | 1,961 | 0
12 months or more - Unrealized (loss) | (102) | 0
Fair Value | 6,430 | 5,130
Unrealized (Loss) | (155) | (180)
Securities held to maturity: |  |
Less than 12 months - Fair value | 6,889 | 12,724
Less than 12 months - Unrealized (loss) | (45) | (211)
12 months or more - Fair value | 0 | 0
12 months or more - Unrealized (loss) | 0 | 0
Fair Value | 6,889 | 12,724
Unrealized (Loss) | $ (45) | (211)
Corporate debt securities |  |
Securities held to maturity: |  |
Less than 12 months - Fair value |  | 1,486
Less than 12 months - Unrealized (loss) |  | (14)
12 months or more - Fair value |  | 0
12 months or more - Unrealized (loss) |  | 0
Fair Value |  | 1,486
Unrealized (Loss) |  | $ (14)

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