REGULATORY CAPITAL (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014 item	Dec. 31, 2013	Mar. 31, 2013	Dec. 31, 2012
REGULATORY CAPITAL
Number of ratios calculated according to the regulations for determining assigned capital category	3
Total capital (to risk-weighted assets)
Actual, Amount	$ 302,272	$ 302,181
Required for Adequate Capital, Amount	145,989	145,150
Actual, Ratio	16.60%	16.70%
Required for Adequate Capital, Ratio	8.00%	8.00%
Tier 1 capital (to risk-weighted assets)
Actual, Amount	279,406	279,440
Required for Adequate Capital, Amount	72,994	72,575
Actual, Ratio	15.30%	15.40%
Required for Adequate Capital, Ratio	4.00%	4.00%
Tier 1 capital (to average assets)
Actual, Amount	279,406	279,440
Required for Adequate Capital, Amount	111,813	110,428
Actual, Ratio (as a percent)	10.00%	10.10%
Required for Adequate Capital, Ratio	4.00%	4.00%
Cash	72,195	61,320	35,897	65,650
Parent Company
Tier 1 capital (to average assets)
Cash	12,000
MainSource Bank
Total capital (to risk-weighted assets)
Actual, Amount	283,825	283,653
Required for Adequate Capital, Amount	144,986	144,147
To Be Well Capitalized, Amount	181,232	180,184
Actual, Ratio	15.70%	15.70%
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	261,116	261,069
Required for Adequate Capital, Amount	72,493	72,074
To Be Well Capitalized, Amount	108,739	108,111
Actual, Ratio	14.40%	14.50%
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	261,116	261,069
Required for Adequate Capital, Amount	110,476	109,090
To Be Well Capitalized, Amount	$ 138,095	$ 136,363
Actual, Ratio (as a percent)	9.50%	9.60%
Required for Adequate Capital, Ratio	4.00%	4.00%
To Be Well Capitalized, Ratio	5.00%	5.00%