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Borrowings - Additional information (Details) $ in Thousands |  |  | 1 Months Ended | 3 Months Ended | 12 Months Ended |
--- | --- | --- | --- | --- | --- | ---
Feb. 24, 2023 USD ($) | Feb. 24, 2020 USD ($) | Dec. 31, 2016 | Jun. 30, 2023 USD ($) | Jun. 30, 2021 USD ($) | Dec. 31, 2023 USD ($) item | Dec. 31, 2022 USD ($) | Dec. 31, 2021 USD ($) | Dec. 31, 2018 USD ($)
Borrowings |  |  |  |  |  |  |  |  |
Securities available-for-sale, at fair value |  |  |  |  |  | $ 1,192,829 | $ 1,539,359 |  |
Threshold percentage of stockholders' equity |  |  |  |  |  | 10.00% |  |  |
Borrowings at FHLBC as percentage of total assets |  |  |  |  |  | 35.00% |  |  |
FHLBC stock |  |  |  |  |  | $ 18,500 | 5,600 |  |
Federal Home Loan Bank Chicago ("FHLBC") and Federal Reserve Bank Chicago ("FRBC") stock |  |  |  |  |  | 33,355 | 20,530 |  |
Proceeds from term note |  | $ 30,000 |  |  |  |  |  |  |
Repayment of term note |  |  |  |  |  | 9,000 | 4,000 | $ 4,000 |
Senior notes |  |  |  |  |  |  | 44,585 |  |
Basis points added to reference rate (as a percent) |  | 1.75% |  |  |  |  |  |  |
Outstanding, net of deferred issuance costs |  |  |  |  |  | 59,400 | 59,300 |  |
Effective interest rate |  | 6.32% |  |  |  |  |  |  |
Total borrowings |  |  |  |  |  | 516,625 | 260,811 |  |
Asset Pledged as Collateral with Right | Securities sold under repurchase agreements |  |  |  |  |  |  |  |  |
Borrowings |  |  |  |  |  |  |  |  |
Investment securities pledged with financial institutions, dollars |  |  |  |  |  | 45,700 | 71,400 |  |
GCFC/ABC Bank |  |  |  |  |  |  |  |  |
Borrowings |  |  |  |  |  |  |  |  |
Debt assumed |  |  |  |  |  |  |  |  | $ 23,400
Balance of borrowings paid off |  |  |  |  |  |  |  | $ 5,900 |
Securities sold under repurchase agreements |  |  |  |  |  |  |  |  |
Borrowings |  |  |  |  |  |  |  |  |
Investment securities pledged with financial institutions, dollars |  |  |  |  |  | $ 26,500 | 32,200 |  |
Number of customers having secured balances exceeding specified percentage of stockholders equity | item |  |  |  |  |  | 0 |  |  |
Total borrowings |  |  |  |  |  | $ 26,470 | 32,156 |  |
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 |  |  |  |  |  |  |  |  |
Borrowings at FHLBC as percentage of book value of certain mortgage loans |  |  |  |  |  | 60.00% |  |  |
FHLBC advance amount |  |  |  |  |  | $ 405,000 | 90,000 |  |
FHLBC stock |  |  |  |  |  | 18,500 | 5,600 |  |
Principal balance of loans collateralized |  |  |  |  |  | 1,460,000 | 969,100 |  |
Maximum borrowing capacity |  |  |  |  |  | 1,000,000 |  |  |
Combined collateral value |  |  |  |  |  | 1,000,000 |  |  |
Amount available for additional borrowings |  |  |  |  |  | 599,900 |  |  |
Subordinated debentures |  |  |  |  |  |  |  |  |
Borrowings |  |  |  |  |  |  |  |  |
Total borrowings |  |  |  |  |  | 59,382 | 59,297 |  |
Notes Payable to Banks [Member] |  |  |  |  |  |  |  |  |
Borrowings |  |  |  |  |  |  |  |  |
Total borrowings |  |  |  |  |  |  | 9,000 |  |
Junior subordinated debentures |  |  |  |  |  |  |  |  |
Borrowings |  |  |  |  |  |  |  |  |
Total borrowings |  |  |  |  |  | $ 25,773 | $ 25,773 |  |
Senior Notes [Member] |  |  |  |  |  |  |  |  |
Borrowings |  |  |  |  |  |  |  |  |
Interest rate (as a percent) |  |  | 5.75% |  |  |  |  |  |
Debt Instrument, Term |  |  | 10 years |  |  |  |  |  |
Interest rate term |  |  | 5 years |  |  |  |  |  |
Effective interest rate |  |  |  | 9.39% |  |  | 8.62% |  |
Debt issuance costs |  |  |  | $ 362 |  |  |  |  |
Total borrowings |  |  |  |  |  |  | $ 44,585 |  |
Debt instrument redemption price, percentage |  |  |  | 12.85% |  | 100.00% |  |  |
Debt redeemed amount |  |  |  | $ 45,000 |  |  |  |  |
Senior Notes [Member] | Debt Instrument Variable Rate Base LIBOR [Member] |  |  |  |  |  |  |  |  |
Borrowings |  |  |  |  |  |  |  |  |
Basis points added to reference rate (as a percent) |  |  | 3.85% |  |  |  |  |  |
Term Debt |  |  |  |  |  |  |  |  |
Borrowings |  |  |  |  |  |  |  |  |
Proceeds from term note |  | $ 20,000 |  |  |  |  |  |  |
Repayment of term note | $ 9,000 |  |  |  |  |  |  |  |
Debt term |  | 3 years |  |  |  |  |  |  |
Subordinated Notes Due 2031 |  |  |  |  |  |  |  |  |
Borrowings |  |  |  |  |  |  |  |  |
Interest rate (as a percent) |  |  |  |  | 3.50% |  |  |  |
Face amount |  |  |  |  | $ 60,000 |  |  |  |
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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