| **Business Combinations (Merger with CFS Bancorp, Inc. (Citizens))** | 9 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |
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| Merger with CFS Bancorp, Inc. (Citizens)                             |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
| **Business Acquisition [Line Items]**                                |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
| Business Combinations                                                | BUSINESS COMBINATIONSOn May 13, 2013, First Merchants Corporation ("First Merchants") and CFS Bancorp, Inc. ("Citizens") entered into an Agreement of Reorganization and Merger (the "Merger Agreement"), pursuant to which, Citizens will, subject to the terms and conditions of the Merger Agreement, merge with and into First Merchants (the "Merger"), whereupon the separate corporate existence of Citizens will cease and First Merchants will survive.  Immediately following the Merger, Citizens Financial Bank, a federal savings bank and wholly-owned subsidiary of Citizens, will be merged with and into First Merchants Bank, National Association, a national bank and wholly-owned subsidiary of First Merchants, with First Merchants Bank, National Association as the surviving bank.  Based on the closing price of First Merchants' common stock on October 31, 2013 of $18.80 per share, the transaction value is estimated at approximately $134 million.  The transaction is expected to be a tax-free stock exchange for those Citizens shareholders receiving First Merchants' common stock pursuant to the Merger.  Subject to customary closing conditions, the parties anticipate completing the Merger in mid-November 2013.  The Boards of Directors and shareholders of both First Merchants and Citizens have approved the Merger Agreement.  Subject to the terms and conditions of the Merger Agreement, upon the completion of the Merger, each share of outstanding Citizens common stock, $0.01 par value per share, will be converted into 0.65 shares (the "Exchange Ratio") of First Merchants common stock, $0.125 stated value per share.  The Exchange Ratio is subject to adjustments for stock splits, stock dividends, recapitalization, or similar transactions, or as otherwise described in the Merger Agreement.  Immediately prior to the Merger, each outstanding share of Citizens restricted stock will automatically vest and, upon the Merger, will also be converted into First Merchants common stock pursuant to the Exchange Ratio. First Merchants will pay cash in lieu of any fractional shares of First Merchants common stock resulting from exchange of shares of Citizens common stock or restricted stock, all at a price and as adjusted pursuant to the Merger Agreement.  Immediately prior to the Merger, Citizens stock options will fully vest, and, upon the Merger, all Citizens stock options will automatically convert into stock options to purchase First Merchants common stock on the same terms and conditions as were applicable under the terms of the Citizens option plan under which such Citizens options were granted and the applicable award agreements thereunder.  In such a case, the number of shares of First Merchants common stock subject to such converted option will equal the product of (i) the number of shares of Citizens' common stock purchasable upon exercise of the original Citizens option and (ii) the Exchange Ratio, and rounded down to the next whole share.  The price per share to exercise such converted option will equal (i) the exercise price per share of Citizens common stock under the original Citizens option divided by (ii) the Exchange Ratio, and rounded up to the nearest cent. |

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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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