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Investment Securities - Amortized Cost and Estimated Fair Value of Available for Sale Securities (Details) - USD ($) | Sep. 30, 2018 | Dec. 31, 2017 | Sep. 30, 2017
--- | --- | --- | ---
Debt Securities, Available-for-sale [Line Items] |  |  |
Other equity securities | $ 3,257,000 | $ 3,414,000 | $ 3,368,000
Securities available for sale, Amortized Cost | 317,005,000 |  |
Securities available for sale, Unrealized Gains | 77,000 |  |
Securities available for sale, Unrealized Losses | (11,638,000) |  |
Securities available for sale | 305,444,000 |  |
Amortized Cost |  | 303,845,000 | 300,268,000
Unrealized Gains |  | 859,000 | 1,480,000
Unrealized Losses |  | (4,532,000) | (2,749,000)
Fair Value (Estimated) |  | 300,172,000 | 298,999,000
US Treasury and Government [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Amortized Cost | 5,000,000 |  |
Unrealized Gains | 0 |  |
Unrealized Losses | (21,000) |  |
Fair Value (Estimated) | 4,979,000 |  |
Mortgage-backed securities |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Amortized Cost | 303,793,000 |  |
Unrealized Gains | 77,000 |  |
Unrealized Losses | (11,300,000) |  |
Fair Value (Estimated) | 292,570,000 |  |
Amortized Cost |  | 293,689,000 | 290,151,000
Unrealized Gains |  | 722,000 | 1,339,000
Unrealized Losses |  | (4,422,000) | (2,701,000)
Fair Value (Estimated) |  | 289,989,000 | 288,789,000
State and political subdivisions |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Amortized Cost | 4,955,000 |  |
Unrealized Gains | 0 |  |
Unrealized Losses | (317,000) |  |
Fair Value (Estimated) | $ 4,638,000 |  |
Amortized Cost |  | 6,860,000 | 6,860,000
Unrealized Gains |  | 16,000 | 28,000
Unrealized Losses |  | (107,000) | (46,000)
Fair Value (Estimated) |  | 6,769,000 | 6,842,000
Other equity securities |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Amortized Cost |  | 3,296,000 | 3,257,000
Unrealized Gains |  | 121,000 | 113,000
Unrealized Losses |  | (3,000) | (2,000)
Fair Value (Estimated) |  | $ 3,414,000 | $ 3,368,000

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