Regulatory & Capital Matters (Details) (USD $)	6 Months Ended		6 Months Ended				6 Months Ended
	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2012 OCC Consent Order Plan	Sep. 30, 2011 OCC Consent Order Plan Minimum	Jun. 30, 2012 Bank of America credit facility, subordinated debt	Dec. 31, 2011 Bank of America credit facility, subordinated debt	Jun. 30, 2012 Junior subordinated debentures quarter businesstrust	Dec. 31, 2011 Junior subordinated debentures	Jun. 30, 2012 Old Second National Bank	Dec. 31, 2011 Old Second National Bank
Regulatory & Capital Matters
Written strategic plan term (in years)			3 years
Tier One leverage ratio, basis point increase (as a percent)									0.01%
Actual over target Tier One leverage ratio, basis point increase (as a percent)									0.60%
Risk-based capital ratio, basis point increase (as a percent)									0.28%
Actual over target risk-based capital ratio, basis point increase (as a percent)									2.00%
Total capital to risk weighted assets, Amount
Actual at period end	$ 188,454,000	$ 191,439,000							$ 202,322,000	$ 200,716,000
Minimum Required for Capital Adequacy Purposes	122,273,000	123,709,000							122,157,000	123,803,000
Minimum Required to Be Well Capitalized									152,696,000	154,754,000
Total capital to risk weighted assets, Ratio
Risk-based capital ratio (as a percent)	12.33%	12.38%		11.25%					13.25%	12.97%
Minimum Required for Capital Adequacy Purposes (as a percent)	8.00%	8.00%							8.00%	8.00%
Minimum Required to Be Well Capitalized (as a percent)									10.00%	10.00%
Tier 1 capital to risk weighted assets, Amount
Actual	94,230,000	95,986,000							182,985,000	180,981,000
Minimum Required for Capital Adequacy Purposes	61,188,000	61,827,000							61,046,000	61,874,000
Minimum Required to Be Well Capitalized									91,569,000	92,811,000
Tier 1 capital to risk weighted assets, Ratio
Actual (as a percent)	6.16%	6.21%							11.99%	11.70%
Minimum Required for Capital Adequacy Purposes (as a percent)	4.00%	4.00%							4.00%	4.00%
Minimum Required to Be Well Capitalized (as a percent)									6.00%	6.00%
Tier 1 capital to average assets, Amount
Actual	94,230,000	95,986,000							182,985,000	180,981,000
Minimum Required for Capital Adequacy Purposes	78,362,000	77,097,000							78,282,000	77,508,000
Minimum Required to Be Well Capitalized									97,853,000	96,885,000
Tier 1 capital to average assets, Ratio
Tier 1 capital leverage ratio (as a percent)	4.81%	4.98%		8.75%					9.35%	9.34%
Minimum Required for Capital Adequacy Purposes (as a percent)	4.00%	4.00%							4.00%	4.00%
Minimum Required to Be Well Capitalized (as a percent)									5.00%	5.00%
Other regulatory capital information
Subordinated debt	45,000,000	45,000,000			45,000,000	45,000,000
Trust preferred proceeds qualified as Tier 1 regulatory capital					24,700,000	25,900,000
Trust preferred proceeds qualified as Tier 2 regulatory capital					31,900,000	30,700,000
Dividend Restrictions and Deferrals
Number of previous years retained profit considered for dividend payment	2 years
Junior subordinated debenture	58,378,000	58,378,000					58,400,000	58,400,000
Number of statutory business trusts that hold junior subordinated debentures							2
Interest payment per year, approximate							4,900,000
Number of quarterly periods for deferral of interest							20
Total amount of deferred and unpaid interest							9,200,000
Deferred preferred stock dividends	$ 7,100,000