REGULATORY CAPITAL (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Total capital (to risk-weighted assets)
Actual, Amount	$ 356,210	$ 332,726
Required for Adequate Capital, Amount	$ 184,170	$ 165,975
Actual, Ratio	15.50%	16.00%
Required for Adequate Capital, Ratio	8.00%	8.00%
Tier 1 capital (to risk-weighted assets)
Actual, Amount	$ 334,190	$ 309,476
Required for Adequate Capital, Amount	$ 138,127	$ 82,988
Actual, Ratio	14.50%	14.90%
Required for Adequate Capital, Ratio	6.00%	4.00%
Common equity Tier 1 capital (to risk-weighted assets)
Actual, Amount	$ 293,316
Required for Adequate Capital, Amount	$ 103,595
Actual, Ratio	12.70%
Required for Adequate Capital, Ratio	4.50%
Tier 1 capital (to average assets)
Actual, Amount	$ 334,190	$ 309,476
Required for Adequate Capital, Amount	$ 130,845	$ 121,014
Actual, Ratio (as a percent)	10.20%	10.20%
Required for Adequate Capital, Ratio	4.00%	4.00%
MainSource Bank
Basel III and Dodd Frank Rules
Tier 1 leverage capital required to be well capitalized to average assets (as a percent)	5.00%	5.00%
Total capital (to risk-weighted assets)
Actual, Amount	$ 334,266	$ 321,005
Required for Adequate Capital, Amount	184,168	164,648
To Be Well Capitalized, Amount	$ 230,211	$ 205,810
Actual, Ratio	14.50%	15.60%
Required for Adequate Capital, Ratio	8.00%	8.00%
To Be Well Capitalized, Ratio	10.00%	10.00%
Tier 1 capital (to risk-weighted assets)
Actual, Amount	$ 312,246	$ 297,755
Required for Adequate Capital, Amount	138,126	82,324
To Be Well Capitalized, Amount	$ 184,168	$ 123,486
Actual, Ratio	13.60%	14.50%
Required for Adequate Capital, Ratio	6.00%	4.00%
To Be Well Capitalized, Ratio	8.00%	6.00%
Common equity Tier 1 capital (to risk-weighted assets)
Actual, Amount	$ 312,246
Required for Adequate Capital, Amount	103,595
To Be Well Capitalized, Amount	$ 149,637
Actual, Ratio	13.60%
Required for Adequate Capital, Ratio	4.50%
To Be Well Capitalized, Ratio	6.50%
Tier 1 capital (to average assets)
Actual, Amount	$ 312,246	$ 297,755
Required for Adequate Capital, Amount	130,555	119,880
To Be Well Capitalized, Amount	$ 163,194	$ 149,850
Actual, Ratio (as a percent)	9.60%	9.90%
Required for Adequate Capital, Ratio	4.00%	4.00%
To Be Well Capitalized, Ratio	5.00%	5.00%