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SUBORDINATED DEBENTURES - Narrative (Details) $ / shares in Thousands | 6 Months Ended | 12 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | ---
Jun. 30, 2018 USD ($) trust $ / shares | Dec. 31, 2017 | Jul. 31, 2017 USD ($) | May 31, 2017 USD ($) | Dec. 31, 2015 USD ($) | Jul. 31, 2015 USD ($)
Federal Home Loan Bank advances |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Debenture term | 30 years |  |  |  |  |
Federal Home Loan Bank advances | Trust II Debentures |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Debenture issued | $ 3,093,000 |  |  |  |  |
Federal Home Loan Bank advances | Trust II Debentures | Minimum |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Notice period required for redemption of debentures | 30 days |  |  |  |  |
Federal Home Loan Bank advances | Trust II Debentures | Maximum |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Notice period required for redemption of debentures | 60 days |  |  |  |  |
Redemption price of debentures as a percentage of principal | 100.00% |  |  |  |  |
Federal Home Loan Bank advances | Trust II Debentures | 3 Month LIBOR |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Spread on variable rate | 3.35% |  |  |  |  |
Federal Home Loan Bank advances | Trust III Debentures |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Debenture issued | $ 2,062,000 |  |  |  |  |
Federal Home Loan Bank advances | Trust III Debentures | Minimum |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Notice period required for redemption of debentures | 30 days |  |  |  |  |
Federal Home Loan Bank advances | Trust III Debentures | Maximum |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Notice period required for redemption of debentures | 60 days |  |  |  |  |
Redemption price of debentures as a percentage of principal | 100.00% |  |  |  |  |
Federal Home Loan Bank advances | Trust III Debentures | 3 Month LIBOR |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Spread on variable rate | 1.67% | 1.67% |  |  |  |
Federal Home Loan Bank advances | DCB Trust I Debentures |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Debenture issued | $ 5,155,000 |  |  |  |  |
Federal Home Loan Bank advances | DCB Trust I Debentures | Minimum |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Notice period required for redemption of debentures | 30 days |  |  |  |  |
Federal Home Loan Bank advances | DCB Trust I Debentures | Maximum |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Notice period required for redemption of debentures | 60 days |  |  |  |  |
Redemption price of debentures as a percentage of principal | 100.00% |  |  |  |  |
Federal Home Loan Bank advances | DCB Trust I Debentures | 3 Month LIBOR |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Spread on variable rate | 1.80% |  |  |  |  |
Federal Home Loan Bank advances | Other Debentures Issued in July 2015 |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Notice period required for redemption of debentures | 30 days |  |  |  |  |
Redemption price of debentures as a percentage of principal | 100.00% |  |  |  |  |
Debenture issued |  |  |  |  |  | $ 4,000,000
Federal Home Loan Bank advances | Other Debentures Issued in July 2015 | Directors and Related Parties |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Debenture issued |  |  |  | $ 2,000,000 |  | $ 3,000,000
Federal Home Loan Bank advances | Other Subordinated Debentures, 2.50% |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Debenture issued, par value per instrument issued |  |  | $ 500,000 |  |  |
Stated interest rate | 25.00% |  | 2.50% |  |  |
Federal Home Loan Bank advances | Other Subordinated Debentures, 4.00% |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Debenture issued, par value per instrument issued | $ 500,000 |  |  |  |  |
Stated interest rate | 4.00% |  |  |  |  |
Federal Home Loan Bank advances | Other Debentures Issued in December 2015 |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Notice period required for redemption of debentures | 30 days |  |  |  |  |
Redemption price of debentures as a percentage of principal | 100.00% |  |  |  |  |
Debenture issued | $ 3,000,000 |  |  |  | $ 5,000,000 |
Debenture issued, par value per instrument issued | $ 500,000 |  |  |  |  |
Federal Home Loan Bank advances | Other Debentures Issued in December 2015 | Directors and Related Parties |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Debenture issued |  |  |  |  | $ 2,500,000 |
Federal Home Loan Bank advances | Other Debentures Issued in December 2015 | Minimum |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Stated interest rate | 3.00% |  |  |  |  |
Federal Home Loan Bank advances | Other Debentures Issued in December 2015 | Maximum |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Stated interest rate | 5.00% |  |  |  |  |
Capital trust pass-through securities |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Number of trusts | trust | 3 |  |  |  |  |
Liquidation value per share (in USD per share) | $ / shares | $ 1,000 |  |  |  |  |

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