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Borrowings - Additional information (Details) | 12 Months Ended |
--- | --- | ---
Dec. 31, 2018 USD ($) item | Dec. 31, 2017 USD ($) | Apr. 20, 2018 USD ($)
Borrowings |  |  |
Threshold percentage of stockholders' equity | 10.00% |  |
Borrowings at FHLBC as percentage of total assets | 35.00% |  |
Bank owned FHLBC stock | $ 7,200,000 | $ 5,400,000 |
Fair value of securities collateralized | 77,600,000 |  |
Principal balance of loans collateralized | 306,200,000 |  |
Maximum borrowing capacity | 304,000,000 |  |
Amount available for additional borrowings | 69,600,000 |  |
Senior notes | 44,158,000 | 44,058,000 |
Debt issuance costs | 692,000 | 739,000 |
Total borrowings | 313,355,000 | 246,615,000 |
GCFC/ABC Bank |  |  |
Borrowings |  |  |
FHLBC advance amount | 15,400,000 |  |
Subordinated Debt. | $ 304,800,000 |  | $ 6,600,000
Debt Instrument, Term | 7 years 3 months |  |
Debt assumed | $ 23,400,000 |  |
GCFC/ABC Bank | Minimum |  |  |
Borrowings |  |  |
Interest rate (as a percent) | 1.40% |  |
GCFC/ABC Bank | Maximum |  |  |
Borrowings |  |  |
Interest rate (as a percent) | 2.83% |  |
Securities sold under repurchase agreements |  |  |
Borrowings |  |  |
Carrying amount of securities secured | $ 46,600,000 | 29,900,000 |
Fair value of the pledged collateral | $ 72,800,000 | 40,000,000 |
Number of customers having secured balances exceeding specified percentage of stockholders equity | item | 0 |  |
Total borrowings | $ 46,632,000 | 29,918,000 |
Securities sold under repurchase agreements | Minimum |  |  |
Borrowings |  |  |
Maturity | 1 day |  |
Securities sold under repurchase agreements | Maximum |  |  |
Borrowings |  |  |
Maturity | 90 days |  |
FHLBC advances |  |  |
Borrowings |  |  |
FHLBC advance amount | $ 149,500,000 | 115,000,000 |
Total borrowings | $ 149,500,000 | $ 115,000,000 |
FHLB advances at 1.42 % |  |  |
Borrowings |  |  |
Interest rate (as a percent) | 2.52% | 1.42% |
FHLBC advance amount | $ 130,000,000 | $ 110,000,000 |
FHLB advances at 1.44 % |  |  |
Borrowings |  |  |
Interest rate (as a percent) | 1.95% | 1.44% |
FHLBC advance amount | $ 15,500,000 | $ 5,000,000 |
Notes payable and other borrowings |  |  |
Borrowings |  |  |
Total borrowings | 15,379,000 |  |
Junior subordinated debentures |  |  |
Borrowings |  |  |
Total borrowings | $ 57,686,000 | 57,639,000 |
Senior Notes. |  |  |
Borrowings |  |  |
Interest rate (as a percent) | 5.75% |  |
Debt Instrument, Term | 10 years |  |
Interest rate term | 5 years |  |
Debt issuance costs | $ 842,000 | $ 942,000 |
Amortization period for deferred financing costs |  | 10 years |
Total borrowings | $ 44,158,000 | $ 44,058,000 |
Senior Notes. | Three month LIBOR |  |  |
Borrowings |  |  |
Basis points added to reference rate (as a percent) | 385.00% |  |

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