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Securities - Summary of Investments in an Unrealized Loss Position that were Temporarily Impaired (Detail) - USD ($) $ in Thousands | Mar. 31, 2018 | Dec. 31, 2017
--- | --- | ---
Securities available for sale: |  |
Less than 12 months - Fair value | $ 54,988 | $ 34,432
Less than 12 months - Unrealized (loss) | (1,090) | (339)
12 months or more - Fair value | 31,045 | 32,323
12 months or more - Unrealized (loss) | (1,421) | (1,153)
Fair Value | 86,033 | 66,755
Unrealized (Loss) | (2,511) | (1,492)
Securities held to maturity: |  |
Less than 12 months - Fair value | 29,932 | 25,190
Less than 12 months - Unrealized (loss) | (673) | (250)
12 months or more - Fair value | 12,497 | 13,297
12 months or more - Unrealized (loss) | (506) | (346)
Fair Value | 42,429 | 38,487
Unrealized (Loss) | (1,179) | (596)
Total securities, Less than 12 months - Fair value | 84,920 | 59,622
Total securities, Less than 12 months - Unrealized (loss) | (1,763) | (589)
Total securities, 12 months or more - Fair value | 43,542 | 45,620
Total securities, 12 months or more - Unrealized (loss) | (1,927) | (1,499)
Total securities, Total fair value | 128,462 | 105,242
Total unrealized (loss) | (3,690) | (2,088)
U.S. agency and mortgage-backed securities |  |
Securities available for sale: |  |
Less than 12 months - Fair value | 47,868 | 29,963
Less than 12 months - Unrealized (loss) | (941) | (286)
12 months or more - Fair value | 29,121 | 30,362
12 months or more - Unrealized (loss) | (1,284) | (1,051)
Fair Value | 76,989 | 60,325
Unrealized (Loss) | (2,225) | (1,337)
Securities held to maturity: |  |
Less than 12 months - Fair value | 17,269 | 18,301
Less than 12 months - Unrealized (loss) | (478) | (205)
12 months or more - Fair value | 12,497 | 13,297
12 months or more - Unrealized (loss) | (506) | (346)
Fair Value | 29,766 | 31,598
Unrealized (Loss) | (984) | (551)
Obligations of states and political subdivisions |  |
Securities available for sale: |  |
Less than 12 months - Fair value | 7,120 | 4,469
Less than 12 months - Unrealized (loss) | (149) | (53)
12 months or more - Fair value | 1,924 | 1,961
12 months or more - Unrealized (loss) | (137) | (102)
Fair Value | 9,044 | 6,430
Unrealized (Loss) | (286) | (155)
Securities held to maturity: |  |
Less than 12 months - Fair value | 11,166 | 6,889
Less than 12 months - Unrealized (loss) | (192) | (45)
12 months or more - Fair value | 0 | 0
12 months or more - Unrealized (loss) | 0 | 0
Fair Value | 11,166 | 6,889
Unrealized (Loss) | (192) | $ (45)
Corporate debt securities |  |
Securities held to maturity: |  |
Less than 12 months - Fair value | 1,497 |
Less than 12 months - Unrealized (loss) | (3) |
12 months or more - Fair value | 0 |
12 months or more - Unrealized (loss) | 0 |
Fair Value | 1,497 |
Unrealized (Loss) | $ (3) |

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