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Securities - Summary of Investments in an Unrealized Loss Position that were Temporarily Impaired (Detail) - USD ($) $ in Thousands | Sep. 30, 2018 | Dec. 31, 2017
--- | --- | ---
Securities available for sale: |  |
Less than 12 months - Fair value | $ 63,455 | $ 34,432
Less than 12 months - Unrealized (loss) | (1,462) | (339)
12 months or more - Fair value | 34,806 | 32,323
12 months or more - Unrealized (loss) | (2,026) | (1,153)
Fair Value | 98,261 | 66,755
Unrealized (Loss) | (3,488) | (1,492)
Securities held to maturity: |  |
Less than 12 months - Fair value | 22,628 | 25,190
Less than 12 months - Unrealized (loss) | (654) | (250)
12 months or more - Fair value | 18,676 | 13,297
12 months or more - Unrealized (loss) | (885) | (346)
Fair Value | 41,304 | 38,487
Unrealized (Loss) | (1,539) | (596)
Total securities, Less than 12 months - Fair value | 86,083 | 59,622
Total securities, Less than 12 months - Unrealized (loss) | (2,116) | (589)
Total securities, 12 months or more - Fair value | 53,482 | 45,620
Total securities, 12 months or more - Unrealized (loss) | (2,911) | (1,499)
Total securities, Total fair value | 139,565 | 105,242
Total unrealized (loss) | (5,027) | (2,088)
U.S. agency and mortgage-backed securities |  |
Securities available for sale: |  |
Less than 12 months - Fair value | 55,198 | 29,963
Less than 12 months - Unrealized (loss) | (1,315) | (286)
12 months or more - Fair value | 31,743 | 30,362
12 months or more - Unrealized (loss) | (1,782) | (1,051)
Fair Value | 86,941 | 60,325
Unrealized (Loss) | (3,097) | (1,337)
Securities held to maturity: |  |
Less than 12 months - Fair value | 8,687 | 18,301
Less than 12 months - Unrealized (loss) | (334) | (205)
12 months or more - Fair value | 18,338 | 13,297
12 months or more - Unrealized (loss) | (874) | (346)
Fair Value | 27,025 | 31,598
Unrealized (Loss) | (1,208) | (551)
Obligations of states and political subdivisions |  |
Securities available for sale: |  |
Less than 12 months - Fair value | 8,257 | 4,469
Less than 12 months - Unrealized (loss) | (147) | (53)
12 months or more - Fair value | 3,063 | 1,961
12 months or more - Unrealized (loss) | (244) | (102)
Fair Value | 11,320 | 6,430
Unrealized (Loss) | (391) | (155)
Securities held to maturity: |  |
Less than 12 months - Fair value | 12,452 | 6,889
Less than 12 months - Unrealized (loss) | (309) | (45)
12 months or more - Fair value | 338 | 0
12 months or more - Unrealized (loss) | (11) | 0
Fair Value | 12,790 | 6,889
Unrealized (Loss) | (320) | $ (45)
Corporate debt securities |  |
Securities held to maturity: |  |
Less than 12 months - Fair value | 1,489 |
Less than 12 months - Unrealized (loss) | (11) |
12 months or more - Fair value | 0 |
12 months or more - Unrealized (loss) | 0 |
Fair Value | 1,489 |
Unrealized (Loss) | $ (11) |

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