Securities (Details) (USD $)	6 Months Ended	12 Months Ended
	Jun. 30, 2012	Dec. 31, 2011
Securities
FHLBC stock	$ 7,400,000	$ 9,300,000
Decrease in FHLBC stock		1,900,000
FRB stock	4,800,000	4,800,000
Available-for-sale securities
Amortized Cost	405,635,000	313,858,000
Gross Unrealized Gains	4,173,000	3,775,000
Gross Unrealized Losses	(10,913,000)	(10,069,000)
Fair Value	398,895,000	307,564,000
Amortized Cost
Due in one year or less	8,256,000
Due after one year through five years	48,540,000
Due after five years through ten years	17,283,000
Due after ten years	19,957,000
Debt securities excluding securities not due at a single maturity date	94,036,000
Total	405,635,000	313,858,000
Weighted Average Yield
Due in one year or less (as a percent)	1.81%
Due after one year through five years (as a percent)	2.01%
Due after five years through ten years (as a percent)	3.18%
Due after ten years (as a percent)	4.04%
Debt securities (as a percent)	2.64%
Total (as a percent)	2.08%
Fair Value
Due in one year or less	8,291,000
Due after one year through five years	48,981,000
Due after five years through ten years	18,043,000
Due after ten years	20,148,000
Debt securities	95,463,000
Total	398,895,000	307,564,000
U.S. Treasury
Available-for-sale securities
Amortized Cost	1,501,000	1,501,000
Gross Unrealized Gains	14,000	23,000
Fair Value	1,515,000	1,524,000
Amortized Cost
Total	1,501,000	1,501,000
Fair Value
Total	1,515,000	1,524,000
U.S. government agencies
Available-for-sale securities
Amortized Cost	44,482,000	43,112,000
Gross Unrealized Gains	173,000	286,000
Gross Unrealized Losses	(32,000)
Fair Value	44,623,000	43,398,000
Amortized Cost
Total	44,482,000	43,112,000
Fair Value
Total	44,623,000	43,398,000
U.S. government agency mortgage-backed
Available-for-sale securities
Amortized Cost	93,458,000	152,473,000
Gross Unrealized Gains	1,766,000	1,553,000
Gross Unrealized Losses	(16,000)	(19,000)
Fair Value	95,208,000	154,007,000
Amortized Cost
Total	93,458,000	152,473,000
Fair Value
Total	95,208,000	154,007,000
States and political subdivisions
Available-for-sale securities
Amortized Cost	12,926,000	12,152,000
Gross Unrealized Gains	1,137,000	1,657,000
Gross Unrealized Losses	(5,000)
Fair Value	14,058,000	13,809,000
Amortized Cost
Total	12,926,000	12,152,000
Fair Value
Total	14,058,000	13,809,000
Corporate bonds
Available-for-sale securities
Amortized Cost	35,127,000	32,357,000
Gross Unrealized Gains	240,000	14,000
Gross Unrealized Losses	(100,000)	(982,000)
Fair Value	35,267,000	31,389,000
Amortized Cost
Total	35,127,000	32,357,000
Fair Value
Total	35,267,000	31,389,000
Collateralized mortgage obligations
Available-for-sale securities
Amortized Cost	62,890,000	25,616,000
Gross Unrealized Gains	367,000	242,000
Gross Unrealized Losses	(870,000)	(736,000)
Fair Value	62,387,000	25,122,000
Amortized Cost
Total	62,890,000	25,616,000
Fair Value
Total	62,387,000	25,122,000
Asset-backed securities
Available-for-sale securities
Amortized Cost	137,341,000	28,755,000
Gross Unrealized Gains	476,000
Gross Unrealized Losses	(1,143,000)	(414,000)
Fair Value	136,674,000	28,341,000
Amortized Cost
Securities not due at a single maturity date	137,341,000
Total	137,341,000	28,755,000
Weighted Average Yield
Securities not due at a single maturity date, Weighted Average Yield (as a percent)	1.63%
Fair Value
Securities not due at a single maturity date	137,674,000
Total	136,674,000	28,341,000
Collateralized debt obligations
Available-for-sale securities
Amortized Cost	17,910,000	17,892,000
Gross Unrealized Losses	(8,747,000)	(7,918,000)
Fair Value	9,163,000	9,974,000
Amortized Cost
Securities not due at a single maturity date	17,910,000	17,892,000
Total	17,910,000	17,892,000
Weighted Average Yield
Securities not due at a single maturity date, Weighted Average Yield (as a percent)	1.89%
Fair Value
Securities not due at a single maturity date	9,163,000	9,974,000
Total	9,163,000	9,974,000
Mortgage backed securities
Amortized Cost
Securities not due at a single maturity date	156,348,000
Weighted Average Yield
Securities not due at a single maturity date, Weighted Average Yield (as a percent)	2.17%
Fair Value
Securities not due at a single maturity date	$ 157,595,000