Fair Value - Carrying Amount and Estimated Fair Value of Finanical Instruments (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Valuation Allowances and Reserves, Balance	$ (261,000)	$ (434,000)
Fair value of mortgage servicing rights	513,000	612,000
Financial assets
Cash and cash equivalents, carrying amount	127,592,000	96,684,000	$ 59,377,000	$ 59,581,000
Cash and Due from Banks	13,572,000	13,053,000
Interest-bearing Deposits in Banks and Other Financial Institutions	114,020,000	83,631,000
Marketable Securities	93,383,000	107,212,000
Securities, carrying amount	92,884,000
Securities, fair value	93,383,000	107,212,000
Loans receivable, net of allowance for loan losses, carrying amounts	1,314,651,000	1,312,952,000
FHLBC stock, carrying amount	8,290,000	11,650,000
Accrued interest receivable, carrying amount	4,619,000	4,381,000
Financial liabilities
Noninterest-bearing demand deposits	234,354,000	249,539,000
Savings deposits	160,501,000	160,002,000
Time Deposits	355,958,000	351,612,000
Borrowings	60,768,000	51,069,000
Carrying Amount [Member]
Financial liabilities
NOW and money market accounts, carrying amount	589,238,000	578,237,000
Accrued interest payable, carrying amount	147,000	102,000
Estimated Fair Value [Member]
Financial assets
Cash and cash equivalents, fair value	127,592,000	96,684,000
Securities, fair value	93,383,000	107,212,000
Loans receivable, net of allowance for loan losses, fair value	1,323,139,000	1,322,947,000
Accounts interest receivable, fair value	4,619,000	4,381,000
Financial liabilities
Non-interest-bearing demand deposits, fair value	234,354,000	249,539,000
NOW money market accounts, fair value	589,238,000	578,237,000
Savings deposits, fair value	160,501,000	160,002,000
Certificates of deposit, fair value	353,969,000	350,593,000
Borrowings, fair value	60,627,000	50,015,000
Accrued interest payable, fair value	147,000	102,000
Estimated Fair Value [Member] | Fair Value, Inputs, Level 1 [Member]
Financial assets
Loans receivable, net of allowance for loan losses, fair value	0	0
Accounts interest receivable, fair value	0	0
Financial liabilities
Non-interest-bearing demand deposits, fair value	0	0
Savings deposits, fair value	0	0
Certificates of deposit, fair value	0	0
Borrowings, fair value	0	0
Accrued interest payable, fair value	0	0
Estimated Fair Value [Member] | Level 2 [Member]
Financial assets
Securities, fair value	92,884,000	106,713,000
Loans receivable, net of allowance for loan losses, fair value	1,323,139,000	1,322,713,000
Accounts interest receivable, fair value	4,619,000	4,381,000
Financial liabilities
Non-interest-bearing demand deposits, fair value	234,354,000	249,539,000
NOW money market accounts, fair value	589,238,000	578,237,000
Savings deposits, fair value	160,501,000	160,002,000
Certificates of deposit, fair value	353,969,000	350,593,000
Borrowings, fair value	60,627,000	50,015,000
Accrued interest payable, fair value	147,000	102,000
Estimated Fair Value [Member] | Fair Value, Inputs, Level 3 [Member]
Financial assets
Cash and cash equivalents, fair value	0	0
Securities, fair value	0	0
Loans receivable, net of allowance for loan losses, fair value	0	234,000
Accounts interest receivable, fair value	0	0
Financial liabilities
Non-interest-bearing demand deposits, fair value	0	0
Savings deposits, fair value	0	0
Certificates of deposit, fair value	0	0
Borrowings, fair value	0	0
Accrued interest payable, fair value	0	0
Equity Funds [Member]
Financial assets
Securities, fair value	499,000	499,000
Fair Value, Measurements, Nonrecurring [Member]
Financial assets
Securities, carrying amount	93,383,000	107,212,000
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 1 [Member]
Financial assets
Securities, carrying amount	499,000	499,000
Fair Value, Measurements, Nonrecurring [Member] | Level 2 [Member]
Financial assets
Securities, carrying amount	92,884,000	106,713,000
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 3 [Member]
Financial assets
Securities, carrying amount	0	0
Fair Value, Measurements, Nonrecurring [Member] | Collateralized Mortgage Obligations Residential [Member]
Financial assets
Securities, carrying amount	4,486,000	$ 5,574,000
Fair Value, Measurements, Nonrecurring [Member] | Collateralized Mortgage Obligations Residential [Member] | Fair Value, Inputs, Level 1 [Member]
Financial assets
Securities, carrying amount	0
Fair Value, Measurements, Nonrecurring [Member] | Collateralized Mortgage Obligations Residential [Member] | Fair Value, Inputs, Level 3 [Member]
Financial assets
Securities, carrying amount	$ 0