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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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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)	3 Months Ended	6 Months Ended
Borrowings - Additional information (Details)	Dec. 31, 2016	Jun. 30, 2018 USD ($) item	Apr. 20, 2018 USD ($)	Dec. 31, 2017 USD ($)
Borrowings
Interest rate (as a percent)	5.75%
Bank owned FHLBC stock		$ 4,300,000		$ 5,400,000
Subordinated Debt.			$ 6,600,000
Senior notes		44,108,000		44,058,000
Debt Instrument, Term	10 years
Interest rate term	5 years
Total borrowings		$ 255,929,000		246,615,000
GCFC/ABC Bank
Borrowings
Debt Instrument, Term		7 years 9 months
Debt assumed		$ 23,500,000
GCFC/ABC Bank \| Minimum
Borrowings
Interest rate (as a percent)		1.40%
GCFC/ABC Bank \| Maximum
Borrowings
Interest rate (as a percent)		2.83%
Three month LIBOR
Borrowings
Basis points added to reference rate (as a percent)	385.00%
Securities sold under repurchase agreements
Borrowings
Carrying amount of securities secured		$ 54,000,000		29,900,000
Fair value of the pledged collateral		$ 73,900,000		40,000,000
Number of customers having secured balances exceeding specified percentage of stockholders equity \| item		1
Total borrowings		$ 54,038,000		29,918,000
Securities sold under repurchase agreements \| Minimum
Borrowings
Threshold percentage of stockholders' equity		10.00%
FHLBC advances
Borrowings
Borrowings at FHLBC as percentage of total assets		35.00%
Borrowings at FHLBC as percentage of book value of certain mortgage loans		60.00%
FHLBC advance amount		$ 72,600,000		115,000,000
Bank owned FHLBC stock		4,300,000
Fair value of securities collateralized		76,700,000
Principal balance of loans collateralized		296,300,000
Combined collateral value		295,500,000
Amount available for additional borrowings		150,100,000
Total borrowings		$ 76,625,000		115,000,000
FHLB advances at 2.01 %
Borrowings
Interest rate (as a percent)		2.01%
FHLBC advance amount		$ 70,000,000
FHLB advances at 1.40 %
Borrowings
Interest rate (as a percent)		1.40%
FHLBC advance amount		$ 2,600,000
Notes payable and other borrowings
Borrowings
Total borrowings		$ 23,496,000
Correspondent Bank
Borrowings
Interest rate (as a percent)		3.73%
Maximum borrowing capacity		$ 20,000,000
Debt Instrument, Term		360 days
Short-term debt		$ 4,000,000
Junior subordinated debentures
Borrowings
Total borrowings		57,662,000		57,639,000
Senior Notes.
Borrowings
Senior notes		44,108,000		44,058,000
Debt issuance costs		$ 892,000		$ 942,000
Amortization period for deferred financing costs		10 years