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Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Transfers from Level 1 to Level 2 | $ 0 | $ 0
Transfers from Level 2 to Level 1 | 0 | 0
Transfers into Level 3 | 0 | 0
Transfers out of Level 3 | 0 | 0
AFS securities [Abstract] |  |
AFS Securities | 1,255,925 | 1,338,290
Trading securities | 11,467 | 9,259
Liabilities [Abstract] |  |
Collateral dependent impaired financing receivable with specific reserves | 100 | 7,000
Reserves on collateral dependent impaired loans | $ 100 | 1,500
Minimum [Member] |  |
Liabilities [Abstract] |  |
Liquidation expense ratio on impaired collateral | 10.00% |
Maximum [Member] |  |
Liabilities [Abstract] |  |
Liquidation expense ratio on impaired collateral | 35.00% |
Federal Agency [Member] |  |
AFS securities [Abstract] |  |
AFS Securities | $ 108,899 | 174,408
State & Municipal [Member] |  |
AFS securities [Abstract] |  |
AFS Securities | 41,956 | 46,726
Other Securities [Member] |  |
AFS securities [Abstract] |  |
AFS Securities | 14,149 | 20,739
Recurring Basis [Member] |  |
AFS securities [Abstract] |  |
AFS Securities | 1,255,925 | 1,338,290
Trading securities | 11,467 | 9,259
Derivatives | 3,732 | 3,210
Total | 1,271,124 | 1,350,759
Liabilities [Abstract] |  |
Derivatives | 324 | 506
Total | 324 | 506
Recurring Basis [Member] | Level 1 [Member] |  |
AFS securities [Abstract] |  |
AFS Securities | 5,845 | 11,493
Trading securities | 11,467 | 9,259
Derivatives | 0 | 0
Total | 17,312 | 20,752
Liabilities [Abstract] |  |
Derivatives | 0 | 0
Total | 0 | 0
Recurring Basis [Member] | Level 2 [Member] |  |
AFS securities [Abstract] |  |
AFS Securities | 1,250,080 | 1,326,797
Trading securities | 0 | 0
Derivatives | 3,732 | 3,210
Total | 1,253,812 | 1,330,007
Liabilities [Abstract] |  |
Derivatives | 324 | 506
Total | 324 | 506
Recurring Basis [Member] | Level 3 [Member] |  |
AFS securities [Abstract] |  |
AFS Securities | 0 | 0
Trading securities | 0 | 0
Derivatives | 0 | 0
Total | 0 | 0
Liabilities [Abstract] |  |
Derivatives | 0 | 0
Total | 0 | 0
Recurring Basis [Member] | Federal Agency [Member] |  |
AFS securities [Abstract] |  |
AFS Securities | 108,899 | 174,408
Recurring Basis [Member] | Federal Agency [Member] | Level 1 [Member] |  |
AFS securities [Abstract] |  |
AFS Securities | 0 | 0
Recurring Basis [Member] | Federal Agency [Member] | Level 2 [Member] |  |
AFS securities [Abstract] |  |
AFS Securities | 108,899 | 174,408
Recurring Basis [Member] | Federal Agency [Member] | Level 3 [Member] |  |
AFS securities [Abstract] |  |
AFS Securities | 0 | 0
Recurring Basis [Member] | State & Municipal [Member] |  |
AFS securities [Abstract] |  |
AFS Securities | 41,956 | 46,726
Recurring Basis [Member] | State & Municipal [Member] | Level 1 [Member] |  |
AFS securities [Abstract] |  |
AFS Securities | 0 | 0
Recurring Basis [Member] | State & Municipal [Member] | Level 2 [Member] |  |
AFS securities [Abstract] |  |
AFS Securities | 41,956 | 46,726
Recurring Basis [Member] | State & Municipal [Member] | Level 3 [Member] |  |
AFS securities [Abstract] |  |
AFS Securities | 0 | 0
Recurring Basis [Member] | Mortgage-Backed [Member] |  |
AFS securities [Abstract] |  |
AFS Securities | 554,927 | 529,844
Recurring Basis [Member] | Mortgage-Backed [Member] | Level 1 [Member] |  |
AFS securities [Abstract] |  |
AFS Securities | 0 | 0
Recurring Basis [Member] | Mortgage-Backed [Member] | Level 2 [Member] |  |
AFS securities [Abstract] |  |
AFS Securities | 554,927 | 529,844
Recurring Basis [Member] | Mortgage-Backed [Member] | Level 3 [Member] |  |
AFS securities [Abstract] |  |
AFS Securities | 0 | 0
Recurring Basis [Member] | Collateralized Mortgage Obligations [Member] |  |
AFS securities [Abstract] |  |
AFS Securities | 535,994 | 566,573
Recurring Basis [Member] | Collateralized Mortgage Obligations [Member] | Level 1 [Member] |  |
AFS securities [Abstract] |  |
AFS Securities | 0 | 0
Recurring Basis [Member] | Collateralized Mortgage Obligations [Member] | Level 2 [Member] |  |
AFS securities [Abstract] |  |
AFS Securities | 535,994 | 566,573
Recurring Basis [Member] | Collateralized Mortgage Obligations [Member] | Level 3 [Member] |  |
AFS securities [Abstract] |  |
AFS Securities | 0 | 0
Recurring Basis [Member] | Other Securities [Member] |  |
AFS securities [Abstract] |  |
AFS Securities | 14,149 | 20,739
Recurring Basis [Member] | Other Securities [Member] | Level 1 [Member] |  |
AFS securities [Abstract] |  |
AFS Securities | 5,845 | 11,493
Recurring Basis [Member] | Other Securities [Member] | Level 2 [Member] |  |
AFS securities [Abstract] |  |
AFS Securities | 8,304 | 9,246
Recurring Basis [Member] | Other Securities [Member] | Level 3 [Member] |  |
AFS securities [Abstract] |  |
AFS Securities | $ 0 | $ 0

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