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Employee Benefit Plans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Old Second Bancorp, Inc. Voluntary Deferred Compensation Plan for Executives
Employee Benefit Plans
Company obligations under Voluntary Deferred Compensation Plan for Executives	$ 1,600	$ 1,900	$ 1,800
Old Second Bancorp Inc Employees 401(k) Savings Plan and Trust
Employee Benefit Plans
Company's discretionary matching contributions to the Plan (as a percent)	100.00%	100.00%	100.00%
Percentage of compensation contributed to the Plan matched by employer	2.00%	2.00%	2.00%
Participants vesting as percentage of discretionary matching contributions	100.00%	100.00%	100.00%
Expense relating to the 401(k) plan	$ 464	$ 477	$ 468

X

- Definition

Aggregate carrying value as of the balance sheet date of the liabilities for all deferred compensation arrangements. Represents currently earned compensation under compensation arrangements that is not actually paid until a later date.

+ References

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- Definition

The amount of the cost recognized during the period for defined contribution plans.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 70
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6414718&loc=d3e28014-114942

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- Definition

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- Definition

Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan.

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- Definition

Percentage employer matches of the employee's percentage contribution matched.

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- Definition

Percentage of employer's matching contributions to a defined contribution plan that vests in a given year.

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