REGULATORY MATTERS (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013 item	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
REGULATORY MATTERS
Number of ratios calculated according to the regulations for determining assigned capital category	3
Number of categories defined in the regulations, ranging from well capitalized to critically undercapitalized	5
Total capital (to risk-weighted assets)
Actual, Amount	$ 302,181	$ 296,714
Required for Adequate Capital, Amount	145,150	133,549
Actual, Ratio	16.70%	17.80%
Required for Adequate Capital, Ratio	8.00%	8.00%
Tier 1 capital (to risk-weighted assets)
Actual, Amount	279,440	275,707
Required for Adequate Capital, Amount	72,575	66,774
Actual, Ratio	15.40%	16.50%
Required for Adequate Capital, Ratio	4.00%	4.00%
Tier 1 capital (to average assets)
Actual, Amount	279,440	275,707
Required for Adequate Capital, Amount	110,428	106,077
Actual, Ratio (as a percent)	10.10%	10.40%
Required for Adequate Capital, Ratio	4.00%	4.00%
Cash	61,320	65,650	109,148	60,123
Parent Company
Tier 1 capital (to average assets)
Cash	11,667	7,102	8,022	14,284
MainSource Bank
Total capital (to risk-weighted assets)
Actual, Amount	283,653	283,303
Required for Adequate Capital, Amount	144,147	132,052
To Be Well Capitalized, Amount	180,184	165,065
Actual, Ratio	15.70%	17.20%
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	261,069	262,527
Required for Adequate Capital, Amount	72,074	66,026
To Be Well Capitalized, Amount	108,111	99,039
Actual, Ratio	14.50%	15.90%
Required for Adequate Capital, Ratio	4.00%	4.00%
To Be Well Capitalized, Ratio	6.00%	6.00%
Tier 1 capital (to average assets)
Actual, Amount	261,069	262,527
Required for Adequate Capital, Amount	109,090	106,077
To Be Well Capitalized, Amount	$ 136,363	$ 132,596
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%