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Borrowings - Additional information (Details) | 3 Months Ended |
--- | --- | ---
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 |  |

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- Definition Represents the amount of borrowings from Federal Home Loan Bank as a percentage of book value of certain mortgage loans. + References No definition available. + Details
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- Definition Represents the amount of borrowings from Federal Home Loan Bank as a percentage of total assets. + References No definition available. + Details
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- Definition Represents the principal balance of loans pledged as collateral in support of federal home loan bank advances outstanding. + References No definition available. + Details
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- Definition Represents the fair value of securities pledged as collateral in support of federal home loan bank advances outstanding + References No definition available. + Details
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- Definition Represents the number of customers having secured balances exceeding specified percentage of stockholders equity. + References No definition available. + Details
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- Definition Amortization period for deferred financing costs. + References No definition available. + Details
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- Definition Represents the threshold percentage which the entity uses for disclosure about the customer holding secured balances. + References No definition available. + Details
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- Definition Contractual interest rate for funds borrowed, under the debt agreement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition 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. + References No definition available. + Details
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- Definition Amount of unused borrowing capacity under the long-term financing arrangement that is available to the entity as of the balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28555-108399 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.17) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Amount of advances from the Federal Home Loan Bank (FHLB). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 470 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6479118&loc=d3e64650-112822 + Details
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- Definition 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). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 325 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=75031641&loc=d3e63345-112809 + Details
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- Definition 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. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 30 -Section 50 -Paragraph 1A -Subparagraph (b)(1)(i) -URI http://asc.fasb.org/extlink&oid=64858031&loc=SL6224234-111729 + Details
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- Definition 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. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.16(a)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.16) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
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- Definition 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. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(16)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(19)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
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