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Borrowings - Additional information (Details)	12 Months Ended
	Dec. 31, 2015 USD ($) item	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Borrowings
Bank owned FHLBC stock	$ 3,700,000	$ 4,300,000
Total borrowings	152,948,000	169,914,000
Securities sold under repurchase agreements
Borrowings
Carrying amount of securities secured	34,100,000	21,000,000
Fair value of the pledged collateral	$ 45,400,000	43,400,000
Number of customers having secured balances exceeding specified percentage of stockholders equity | item	0
Total borrowings	$ 34,070,000	21,036,000
Additional information related to repurchase agreements
Average daily balance during the year	$ 28,194,000	$ 26,093,000	$ 23,313,000
Average interest rate during the year (as a percent)	0.01%	0.01%	0.01%
Maximum month-end balance during the year	$ 34,785,000	$ 38,133,000	$ 30,510,000
Weighted average interest rate at year-end (as a percent)	0.01%	0.01%	0.01%
Securities sold under repurchase agreements | Minimum
Borrowings
Maturity	1 day
Securities sold under repurchase agreements | Maximum
Borrowings
Maturity	90 days
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%
Debt Instrument, Interest Rate, Stated Percentage	0.16%
Bank owned FHLBC stock	$ 3,700,000
Fair value of securities collateralized	98,800,000
Principal balance of loans collateralized	169,700,000
Combined collateral value	190,700,000
Amount available for additional borrowings	174,400,000
Total borrowings	15,000,000	$ 45,000,000
Subordinated debt
Borrowings
Face amount	45,000,000
Total borrowings	$ 45,000,000	45,000,000
Subordinated debt | LIBOR
Borrowings
Variable interest rate base	three-month LIBOR
Basis points added to reference rate (as a percent)	1.50%
Notes payable and other borrowings
Borrowings
Total borrowings	$ 500,000	500,000
Correspondent Bank
Borrowings
Maximum borrowing capacity	$ 45,500,000
Senior debt facility | LIBOR
Borrowings
Basis points added to reference rate (as a percent)	0.90%
Senior debt facility | Prime rate
Borrowings
Variable interest rate base	prime
Term debt
Borrowings
Maximum borrowing capacity	$ 500,000
Basis points added to reference rate (as a percent)	2.00%
Total borrowings	$ 500,000
Junior subordinated debentures
Borrowings
Total borrowings	$ 58,378,000	$ 58,378,000

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