| **Stockholders' Equity** | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
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| **Equity [Abstract]**    |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |
| Stockholders' Equity     | STOCKHOLDERS' EQUITYNational banking laws restrict the maximum amount of dividends that a bank may pay in any calendar year.  National banks are limited to the bank’s retained net income (as defined) for the current year plus those for the previous two years.  The amount at December 31, 2014, available for 2015 dividends from the Corporation’s subsidiaries (both banking and non-banking) was $23,340,000.Total stockholders' equity for all subsidiaries at December 31, 2014, was $818,420,000 of which $795,080,000 was restricted from dividend distribution to the Corporation.The Corporation has a Dividend Reinvestment and Stock Purchase Plan, enabling stockholders to elect to have their cash dividends on all shares automatically reinvested in additional shares of the Corporation’s common stock. In addition, stockholders may elect to make optional cash payments up to an aggregate of $2,500 per quarter for the purchase of additional shares of common stock.  The stock is credited to participant accounts at fair market value.  Dividends are reinvested on a quarterly basis.Preferred StockOn September 22, 2011, the Corporation entered into a Securities Purchase Agreement (the “Purchase Agreement”) with the Treasury, pursuant to which the Corporation issued 90,782.94 shares of the Corporation’s Senior Non-Cumulative Perpetual Preferred Stock, Series B (the “Series B Preferred Stock”), having a liquidation amount per share equal to $1,000, for a total purchase price of $90,782,940. The Purchase Agreement was entered into, and the Series B Preferred Stock was issued, pursuant to the SBLF program, a $30 billion fund established under the Small Business Jobs Act of 2010, that encourages lending to small businesses by providing capital to qualified community banks with assets of less than $10 billion.On January 3, 2013, the Corporation redeemed 22,695.94 shares of the Series B Preferred Stock held by the Treasury at an aggregate redemption price of $22,695,940 plus accrued but unpaid dividends.  Following the redemption, the Treasury held 68,087 shares of the Series B Preferred Stock representing a remaining liquidation amount of approximately $68 million.On July 2, 2013, the Corporation redeemed an additional 34,044 shares of the Series B Preferred Stock held by the Treasury at an aggregate redemption price of $34,044,000 plus accrued but unpaid dividends.  Following the redemption, the Treasury held 34,043 shares of the Series B Preferred Stock representing a remaining liquidation amount of approximately $34 million.On November 22, 2013, the Corporation redeemed the final 34,043 shares of the Series B Preferred Stock held by the Treasury at an aggregate redemption price of $34,043,000 plus accrued but unpaid dividends.  There are no shares of the Corporation's Series B Preferred Stock currently outstanding.CFS AcquisitionOn November 12, 2013, the Corporation acquired 100 percent of CFS Bancorp, Inc. ("CFS") in an all stock transaction.  Pursuant to the merger agreement, the shareholders of CFS received 0.65 percent of a share of the Corporation's common stock for each share of CFS Bancorp common stock held.  The Corporation issued approximately 7.1 million shares of common stock, which was valued at approximately $135.6 million. Community AcquisitionOn November 7, 2014, the Corporation acquired 100 percent of Community Bancshares, Inc. ("Community").  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 First Merchants' 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. |

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| - Definition
The entire disclosure for shareholders' equity comprised of portions attributable to the parent entity and noncontrolling interest, including other comprehensive income. Includes, but is not limited to, balances of common stock, preferred stock, additional paid-in capital, other capital and retained earnings, accumulated balance for each classification of other comprehensive income and amount of comprehensive income.
+ References
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