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Represents the amount of borrowings from Federal Home Loan Bank as a percentage of book value of certain mortgage loans.

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Represents the amount of borrowings from Federal Home Loan Bank as a percentage of total assets.

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Represents the principal balance of loans pledged as collateral in support of federal home loan bank advances outstanding.

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Represents the fair value of securities pledged as collateral in support of federal home loan bank advances outstanding

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Represents the number of customers having secured balances exceeding specified percentage of stockholders equity.

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No definition available.

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Amortization period for deferred financing costs.

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Represents the threshold percentage which the entity uses for disclosure about the customer holding secured balances.

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

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No definition available.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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No definition available.

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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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Represents the aggregate of total long-term debt, including current maturities and short-term debt.

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No definition available.

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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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

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Amount of the collateral pledged in support of federal home loan bank advances outstanding.

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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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The fair value, as of the date of each statement of financial position presented, of securities which are owned but transferred to serve as collateral for the payment of repurchase agreements, and that are reclassified and separately reported in the statement of financial position because the transferee has the right by contract or custom to sell or re-pledge them.

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The carrying amount as of the date of the latest financial statement presented of securities which are owned but transferred to serve as collateral for repurchase agreements, and for which the transferee does not have the right by contract or custom to sell or re-pledge them to an unrelated party.

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Including the current and noncurrent portions, carrying value as of the balance sheet date of Notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer). Senior note holders are paid off in full before any payments are made to junior note holders.

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Including the current and noncurrent portions, carrying value as of the balance sheet date of subordinated debt (with initial maturities beyond one year or beyond the operating cycle if longer). Subordinated debt places a lender in a lien position behind debt having a higher priority of repayment in liquidation of the entity's assets.

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Borrowings - Additional information (Details)	3 Months Ended
Borrowings - Additional information (Details)	Mar. 31, 2018 USD ($) item	Dec. 31, 2016	Dec. 31, 2017 USD ($)
Borrowings
Semi annual interest rate		5.75%
Bank owned FHLBC stock	$ 2,700,000		$ 5,400,000
Subordinated Debt.	6,600,000
Senior notes	44,083,000		44,058,000
Debt Instrument, Term		10 years
Interest rate term		5 years
Total borrowings	188,099,000		246,615,000
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	41,400,000		29,900,000
Fair value of the pledged collateral	$ 49,300,000		40,000,000
Number of customers having secured balances exceeding specified percentage of stockholders equity \| item	0
Total borrowings	$ 41,366,000		29,918,000
Securities sold under repurchase agreements \| Minimum
Borrowings
Threshold percentage of stockholders' equity	10.00%
FHLBC advances
Borrowings
Fair value of the pledged collateral	$ 80,100,000
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	$ 45,000,000		115,000,000
Bank owned FHLBC stock	2,700,000
Fair value of securities collateralized	80,100,000
Principal balance of loans collateralized	290,400,000
Combined collateral value	292,500,000
Amount available for additional borrowings	208,300,000
Total borrowings	45,000,000		115,000,000
Junior subordinated debentures
Borrowings
Total borrowings	57,650,000		57,639,000
Senior Notes.
Borrowings
Debt issuance costs	$ 917,000		$ 942,000
Amortization period for deferred financing costs	10 years