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Borrowings - Additional information (Details) |  |  | 3 Months Ended | 12 Months Ended |
--- | --- | --- | --- | --- | ---
Dec. 31, 2020 USD ($) | Feb. 24, 2020 USD ($) | Jun. 30, 2021 USD ($) | Dec. 31, 2021 USD ($) item | Dec. 31, 2020 USD ($) | Dec. 31, 2018 USD ($)
Borrowings |  |  |  |  |  |
Threshold percentage of stockholders' equity |  |  |  | 10.00% |  |
Borrowings at FHLBC as percentage of total assets |  |  |  | 35.00% |  |
FHLBC stock | $ 3,700,000 |  |  | $ 7,100,000 | $ 3,700,000 |
Federal Home Loan Bank Chicago ("FHLBC") and Federal Reserve Bank Chicago ("FRBC") stock | 9,917,000 |  |  | 13,257,000 | 9,917,000 |
Fair value of securities collateralized |  |  |  | 7,100,000 |  |
Proceeds from term note | 20,000,000.0 | $ 20,000,000.0 |  |  |  |
Cash distribution rate of trust preferred securities (as a percent) |  | 7.80% |  |  |  |
Senior notes | 44,375,000 |  |  | 44,480,000 | 44,375,000 |
Basis points added to reference rate (as a percent) |  | 175.00% |  |  |  |
Debt issuance costs | 1,000 |  |  | 1,000 | 1,000 |
Total borrowings | 160,521,000 |  |  | 198,876,000 | 160,521,000 |
GCFC/ABC Bank |  |  |  |  |  |
Borrowings |  |  |  |  |  |
FHLBC advance amount | $ 6,400,000 |  |  | $ 6,100,000 | $ 6,400,000 |
Debt Instrument, Term |  |  |  | 4 years 3 months | 5 years 3 months |
Debt assumed |  |  |  |  |  | $ 23,400,000
GCFC/ABC Bank | Maximum |  |  |  |  |  |
Borrowings |  |  |  |  |  |
Interest rate (as a percent) | 2.83% |  |  | 2.83% | 2.83% |
Securities sold under repurchase agreements |  |  |  |  |  |
Borrowings |  |  |  |  |  |
Carrying amount of securities secured | $ 67,000,000.0 |  |  | $ 50,300,000 | $ 67,000,000.0 |
Fair value of the pledged collateral | 94,400,000 |  |  | $ 113,000,000.0 | 94,400,000 |
Number of customers having secured balances exceeding specified percentage of stockholders equity | item |  |  |  | 0 |  |
Total borrowings | 66,980,000 |  |  | $ 50,337,000 | 66,980,000 |
Securities sold under repurchase agreements | Minimum |  |  |  |  |  |
Borrowings |  |  |  |  |  |
Maturity |  |  |  | 1 day |  |
Securities sold under repurchase agreements | Maximum |  |  |  |  |  |
Borrowings |  |  |  |  |  |
Maturity |  |  |  | 90 days |  |
Federal Home Loan Bank Advances |  |  |  |  |  |
Borrowings |  |  |  |  |  |
FHLBC advance amount |  |  |  | $ 0 |  |
FHLBC stock | 3,700,000 |  |  | 7,100,000 | 3,700,000 |
Fair value of securities collateralized | 54,700,000 |  |  |  | 54,700,000 |
Principal balance of loans collateralized | 625,800,000 |  |  | 536,900,000 | 625,800,000 |
Maximum borrowing capacity | 390,400,000 |  |  |  | 390,400,000 |
Amount available for additional borrowings |  |  |  | 313,100,000 |  |
Subordinated debentures |  |  |  |  |  |
Borrowings |  |  |  |  |  |
Total borrowings |  |  |  | 59,212,000 |  |
Notes payable and other borrowings |  |  |  |  |  |
Borrowings |  |  |  |  |  |
Total borrowings | 23,393,000 |  |  | 19,074,000 | 23,393,000 |
Junior subordinated debentures |  |  |  |  |  |
Borrowings |  |  |  |  |  |
Total borrowings | 25,773,000 |  |  | $ 25,773,000 | 25,773,000 |
Senior notes |  |  |  |  |  |
Borrowings |  |  |  |  |  |
Interest rate (as a percent) |  |  |  | 5.75% |  |
Senior notes | 44,400,000 |  |  | $ 44,500,000 | 44,400,000 |
Debt Instrument, Term |  |  |  | 10 years |  |
Interest rate term |  |  |  | 5 years |  |
Effective interest rate |  |  |  | 6.06% |  |
Debt issuance costs | 625,000 |  |  | $ 520,000 | 625,000 |
Amortization period for deferred financing costs |  |  |  | 10 years |  |
Total borrowings | 44,375,000 |  |  | $ 44,480,000 | $ 44,375,000 |
Debt instrument redemption price, percentage |  |  |  | 100.00% |  |
Senior notes | Debt Instrument, Variable Rate Base LIBOR [Member] |  |  |  |  |  |
Borrowings |  |  |  |  |  |
Basis points added to reference rate (as a percent) |  |  |  | 385.00% |  |
Term Debt |  |  |  |  |  |
Borrowings |  |  |  |  |  |
Proceeds from term note | $ 13,000,000.0 | $ 20,000,000.0 |  |  |  |
Effective interest rate |  |  |  | 1.85% |  |
Debt term |  |  |  | 3 years |  |
Subordinated Notes Due 2031 |  |  |  |  |  |
Borrowings |  |  |  |  |  |
Interest rate (as a percent) |  |  | 3.50% |  |  |
Outstanding, net of deferred issuance costs |  |  |  | $ 59,200,000 |  |
Face amount |  |  | $ 60,000,000.0 |  |  |
Subordinated Notes Due 2031 | Three Months Secured Overnight Financing Rate |  |  |  |  |  |
Borrowings |  |  |  |  |  |
Basis points added to reference rate (as a percent) |  |  | 2.73% |  |  |

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