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Basis of Accounting and Consolidation Basis of Accounting and Consolidation (Acquisitions) | May 01, 2018 USD ($) $ / shares shares | Dec. 11, 2017 $ / shares shares | Mar. 31, 2018 USD ($) $ / shares | Dec. 31, 2017 USD ($) $ / shares
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Agreement And Plan Of Merger [Abstract] |  |  |  |
Common stock, par value (in dollars per share) | $ / shares |  |  | $ 4 | $ 4
Assets |  |  | $ 2,837,346,000 | $ 2,841,539,000
Gross loans |  |  | 1,983,555,000 | 1,946,114,000
Deposits |  |  | $ 2,291,891,000 | $ 2,274,639,000
First BancTrust [Member] |  |  |  |
Agreement And Plan Of Merger [Abstract] |  |  |  |
Percent Of Acquiree Outstanding Stock Being Acquired In Merger |  | 1.00 |  |
Par Value Of Outstanding Stock Being Acquired In Merger | $ / shares |  |  | $ 0.01 |
Right To Receive Value of Cash Option | $ / shares |  | $ 5.00 |  |
Right To Receive Value Of Share Option | shares |  | 0.800 |  |
Assets |  |  | $ 479,200,000 |
Gross loans |  |  | 369,600,000 |
Deposits |  |  | $ 391,600,000 |
Subsequent Event [Member] | First BancTrust [Member] |  |  |  |
Agreement And Plan Of Merger [Abstract] |  |  |  |
Shares, Issued | shares | 1,643,900 |  |  |
Shares Issued, Price Per Share | $ / shares | $ 37.32 |  |  |
Aggregate Total Of Cash Paid In Business Combination | $ 10,275,000 |  |  |

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- Definition Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(12)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(11)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
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