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The amount of total capital as defined in the regulations.

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The minimum Total risk based capital ratio (total capital divided by risk weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action.

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Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

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Tier 1 Risk Based Capital as defined in the regulations.

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REGULATORY CAPITAL (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015 item	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
REGULATORY CAPITAL
Number of ratios calculated according to the regulations for determining assigned capital category	4
Basel III and Dodd Frank Rules
Required minimum conservation buffer percentage	2.50%
Total capital (to risk-weighted assets)
Actual, Amount	$ 340,061us-gaap_Capital	$ 332,726us-gaap_Capital
Required for Adequate Capital, Amount	165,818	165,975
Actual, Ratio	16.40%us-gaap_CapitalToRiskWeightedAssets	16.00%us-gaap_CapitalToRiskWeightedAssets
Required for Adequate Capital, Ratio	8.00%	8.00%
Tier 1 capital (to risk-weighted assets)
Actual, Amount	317,423us-gaap_TierOneRiskBasedCapital	309,476us-gaap_TierOneRiskBasedCapital
Required for Adequate Capital, Amount	124,364	82,988
Actual, Ratio	15.30%	14.90%
Required for Adequate Capital, Ratio	6.00%	4.00%
Common equity Tier 1 capital (to risk-weighted assets)
Actual, Amount	276,423
Required for Adequate Capital, Amount	93,273
Actual, Ratio	13.30%
Required for Adequate Capital, Ratio	4.50%
Tier 1 capital (to average assets)
Actual, Amount	317,423us-gaap_TierOneLeverageCapital	309,476us-gaap_TierOneLeverageCapital
Required for Adequate Capital, Amount	122,812	121,014
Actual, Ratio (as a percent)	10.30%	10.20%
Required for Adequate Capital, Ratio	4.00%	4.00%
Cash	69,550	62,485	72,195	61,320
Minimum \| Prior To Federal Reserve Corrective Action Rules
Tier 1 capital (to risk-weighted assets)
Required for Adequate Capital, Ratio	4.00%
Minimum \| Federal Reserve Corrective Action Rules
Basel III and Dodd Frank Rules
Required minimum conservation buffer percentage	2.50%
Required minimum Tier 1 capital to risk weighted assets (as a percent )	4.50%
Tier 1 capital (to risk-weighted assets)
Required for Adequate Capital, Ratio	6.00%
Tier 1 capital (to average assets)
Required for Adequate Capital, Ratio	4.00%
Parent Company
Tier 1 capital (to average assets)
Cash	9,000
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	324,236	321,005
Required for Adequate Capital, Amount	166,119	164,648
To Be Well Capitalized, Amount	207,649	205,810
Actual, Ratio	15.60%	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	301,598	297,755
Required for Adequate Capital, Amount	124,590	82,324
To Be Well Capitalized, Amount	166,119	123,486
Actual, Ratio	14.50%	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	301,598
Required for Adequate Capital, Amount	93,442
To Be Well Capitalized, Amount	134,972
Actual, Ratio	14.50%
Required for Adequate Capital, Ratio	4.50%
To Be Well Capitalized, Ratio	6.50%
Tier 1 capital (to average assets)
Actual, Amount	301,598	297,755
Required for Adequate Capital, Amount	121,662	119,880
To Be Well Capitalized, Amount	$ 152,078	$ 149,850
Actual, Ratio (as a percent)	9.90%	9.90%
Required for Adequate Capital, Ratio	4.00%	4.00%
To Be Well Capitalized, Ratio	5.00%	5.00%