| **Business Combinations**            | 3 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  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| **Business Combinations [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 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| Business Combinations                | BUSINESS COMBINATIONSCommunity Bancshares, Inc.On November 7, 2014, the Corporation acquired 100 percent of Community Bancshares, Inc. ("Community").  Community was headquartered in Noblesville, Indiana and had 10 full-service banking centers serving central Indiana.  Pursuant to the merger agreement, each outstanding share of common stock of Community was converted into the right to receive either (a) 4.0926 shares of the Corporation's common stock, plus cash in lieu of fractional shares; or (b) $85.94 in cash, based upon shareholder elections.  The Corporation paid $14.2 million in cash and issued approximately 1.6 million shares of common stock, valued at approximately $35.0 million, for a total purchase price of approximately $49.2 million.The Corporation engaged in this transaction with the expectation that it would be accretive to income and expand the existing footprint in central Indiana.  Goodwill resulted from this transaction due to the expected synergies from combining operations.Under the acquisition method of accounting, the total purchase price is allocated to net tangible and intangible assets based on their current estimated fair values on the date of the acquisition.   Based on preliminary valuations of the fair value of tangible and intangible assets acquired and liabilities assumed, which are based on assumptions that are subject to change, the purchase price for the Community acquisition is detailed in the following table.  Prior to the end of the one year measurement period for finalizing the purchase price allocation, if information becomes available which would indicate adjustments are required to the purchase price allocation, such adjustments will be included in the purchase price allocation retrospectively.  Fair ValueCash and cash equivalents $4,124Interest -bearing time deposits 16,526Investment Securities, available for sale 76,807Loans 145,064Premises and equipment 3,610Federal Home Loan Bank stock 1,950Interest receivable 767Cash surrender value of life insurance 3,266Other real estate owned 6,662Taxes, deferred and receivable 3,348Other assets 167Deposits (228,424)Interest payable (98)Other liabilities (3,014)Net tangible assets acquired 30,755Core deposit intangible 4,658Goodwill 13,776Purchase price $49,189Of the total purchase price, $4,658,000 has been allocated to a core deposit intangible that will be amortized over its estimated life of 10 years.  The remaining purchase price has been allocated to goodwill, which is not deductible for tax purposes.Pro Forma Financial InformationThe Corporation acquired CFS Bancorp ("CFS") on November 12, 2013 and Community on November 7, 2014.  The results of operations of CFS and Community have been included in the Corporation's consolidated financial statements since the acquisition dates.  The following schedule includes pro forma results for the periods ended December 31, 2014 and 2013 as if the CFS and Community acquisitions had occurred as of the beginning of the comparable prior annual reporting period.  2014 2013Total revenue (net interest income plus other income)$263,070 $253,668Net income$61,572 $39,979Net income available to common shareholders$61,572 $37,599Earnings per share:   Basic$1.63 $0.98Diluted$1.61 $0.97The pro forma information includes adjustments for interest income on loans, amortization of intangibles arising from the transaction, interest expense on deposits acquired, premises expense for the banking centers acquired and the related income tax effects.  The pro forma information for the year ended December 31, 2014 includes $1.6 million of operating revenue from Community since the acquisition and approximately $1.8 million, net of tax, of non-recurring expenses directly attributable to the Community acquisition.  The pro forma information for the year ended December 31, 2013 includes $4.9 million of operating revenue from CFS since the acquisition and approximately $9.5 million, net of tax, of non-recurring expenses directly attributable to the CFS acquisition.The pro forma financial information is presented for information purposes only and is not indicative of the results of operations that actually would have been achieved had the acquisition been consummated as of that time, nor is it intended to be a projection of future results.C Financial CorporationThe Corporation and C Financial Corporation ("C Financial") entered into an Agreement and Plan of Reorganization and Merger (the “Merger Agreement”) on January 5, 2015.  On April 17, 2015, the Corporation completed the merger with C Financial, pursuant to which, C Financial merged with and into the Corporation (the “Merger”) whereupon the separate corporate existence of C Financial ceased and the Corporation survived.  Immediately following the Merger, Cooper State Bank, an Ohio state bank and wholly-owned subsidiary of C Financial, merged with and into First Merchants Bank, National Association, a national bank and wholly-owned subsidiary of the Corporation, with First Merchants Bank, National Association continuing as the surviving bank.  As part of the $14.5 million merger, shareholders of C Financial received $6.738 in cash for each share of C Financial common stock held.  As a result of this merger, the Corporation ($5.8 billion) and C Financial ($138 million) have combined assets of approximately $6.0 billion. |

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| - Definition
The entire disclosure for a business combination (or series of individually immaterial business combinations) completed during the period, including background, timing, and recognized assets and liabilities. The disclosure may include leverage buyout transactions (as applicable).
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