| **Subsequent Events**            | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
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| **Subsequent Events [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
| Subsequent Events                | SUBSEQUENT EVENTSMBT Financial Corp.On October 9, 2018, the Corporation and MBT Financial Corp., a Michigan corporation ("MBT"), entered into an Agreement and Plan of Reorganization and Merger (the "Merger Agreement"), pursuant to which MBT will, subject to the terms and conditions of the Merger Agreement, merge with and into the Corporation (the "Holding Company Merger"), whereupon the separate corporate existence of MBT will cease and the Corporation will survive.  Immediately following the Holding Company Merger, MBT's wholly-owned subsidiary, Monroe Bank & Trust, will be merged with and into the Bank (the "Bank Merger" and, together with the Holding Company Merger, the "Mergers"), with the Bank continuing as the surviving bank.  Based on the closing price of the Corporation's common stock on October 9, 2018 of $45.71 per share, the transaction value is estimated at approximately $290.9 million.  The transaction is expected to be a tax-free exchange for MBT's shareholders who will be receiving the Corporation's common stock pursuant to the Holding Company Merger.  MBT's total assets as of December 31, 2018 were $1.3 billion.At a special meeting held on February 14, 2019, the shareholders of MBT approved the Merger Agreement and the transactions contemplated by the Merger Agreement.  In addition, on January 3, 2019, the FDIC issued its order approving the Bank Merger, subject to certain customary conditions, and on February 18, 2019, the Indiana DFI approved the Bank Merger.  However, consummation of the Mergers remain subject to the (i) receipt of a waiver by the Federal Reserve Board of Governors relating to its right to receive an application in connection with the Holding Company Merger, and (ii) satisfaction of other customary closing conditions contained in the Merger Agreement.  The Mergers are expected to close during the first half of 2019. |

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No definition available.
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| - Definition
The entire disclosure for significant events or transactions that occurred after the balance sheet date through the date the financial statements were issued or the date the financial statements were available to be issued. Examples include: the sale of a capital stock issue, purchase of a business, settlement of litigation, catastrophic loss, significant foreign exchange rate changes, loans to insiders or affiliates, and transactions not in the ordinary course of business.
+ References
Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 855 -URI http://asc.fasb.org/topic&trid=2122774
+ Details**Name:**us-gaap_SubsequentEventsTextBlock**Namespace Prefix:**us-gaap_**Data Type:**nonnum:textBlockItemType**Balance Type:**na**Period Type:**duration |