Parent Company Condensed Financial Information - Condensed Balance Sheets (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Assets
Other assets	$ 16,333	$ 15,818
Total assets	2,251,188	2,077,028
Liabilities and Stockholders' Equity
Junior subordinated debentures	57,591	57,543
Senior Notes	43,998
Subordinated debt		45,000
Other liabilities	11,889	9,900
Stockholders' equity	175,210	155,929	$ 194,163	$ 147,692
Total liabilities and stockholders' equity	2,251,188	2,077,028
Old Second Bancorp, Inc.
Assets
Noninterest bearing deposit with bank subsidiary	26,925	33,500
Investment in subsidiaries	228,646	204,509
Other assets	23,304	22,116
Total assets	278,875	260,125
Liabilities and Stockholders' Equity
Junior subordinated debentures	57,591	57,543
Senior Notes	43,998
Subordinated debt		45,000
Other liabilities	2,076	1,653
Stockholders' equity	175,210	155,929
Total liabilities and stockholders' equity	$ 278,875	$ 260,125