| **Contingent Liabilities**                              | 6 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
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| **Commitments and Contingencies Disclosure [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |
| Contingent Liabilities                                  | CONTINGENT LIABILITIESOn April 16, 2013, First Merchants was named in a class action lawsuit in Delaware County Circuit Court challenging First Merchant's checking account practices associated with the assessment of overdraft fees.  The plaintiff seeks damages and other relief, including restitution and injunctive relief.  First Merchants believes it has meritorious defenses to the claims brought by the plaintiff.  First Merchants removed the case from state court to federal district court.  First Merchants also recently filed a motion to stay the federal action pending arbitration.  No discovery has been conducted and no class has been certified.  Accordingly, at this phase of the litigation, it is not possible for management of First Merchants to determine the probability of a material adverse outcome or reasonably estimate the amount of any loss.  On July 30, 2013, a purported shareholder of CFS Bancorp, Inc. filed a putative class action lawsuit captioned Jay Orlando v. CFS Bancorp, Inc., et al., No. 2:13-CV-00261 in U.S. District Court in the Northern District of Indiana against CFS Bancorp, Inc., its board of directors and First Merchants. The complaint generally alleges various claims of federal securities law violations and that the directors of CFS Bancorp, Inc. breached their fiduciary duties by providing materially inadequate disclosures and material disclosure omissions with respect to the proposed merger of CFS Bancorp, Inc. into First Merchants. The plaintiff seeks (1) class certification, (2) to enjoin the merger or, in the event the merger is completed before entry of a final judgment, to rescind the merger or be awarded an unspecified amount of rescissory damages, (3) compensatory damages in an unspecified amount, and (4) costs and expenses, including attorneys' fees. At this early stage of the litigation, it is not possible to assess the probability of a material adverse outcome or reasonably estimate any potential financial impact of the lawsuit on First Merchants. The defendants believe the claims against them are without merit and intend to contest the matter vigorously. |

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| - Definition
The entire disclosure for legal proceedings, legal contingencies, litigation, regulatory and environmental matters and other contingencies.
+ References
No definition available.
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