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Amortization period for deferred financing costs.

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Percentage points added to the reference rate to compute the variable rate on the debt instrument.

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Amount of unused borrowing capacity under the long-term financing arrangement that is available to the entity as of the balance sheet date.

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Amount of advances from the Federal Home Loan Bank (FHLB).

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Federal Home Loan Bank (FHLB) stock represents an equity interest in a FHLB. It does not have a readily determinable fair value because its ownership is restricted and it lacks a market (liquidity).

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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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Borrowings - Additional information (Details)	12 Months Ended
Borrowings - Additional information (Details)	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%