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Allowance for Loan Losses and Credit Quality of Loans, Average Recorded Investments on Loans Specifically Evaluated for Impairment and Interest Income Recognized (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Financing Receivable, Impaired [Line Items] |  |  |
Average recorded investment | $ 23,238 | $ 30,132 | $ 32,470
Interest income recognized accrual | 924 | 970 | 895
Originated Loans [Member] |  |  |
Financing Receivable, Impaired [Line Items] |  |  |
Average recorded investment | 23,145 | 28,927 | 24,691
Interest income recognized accrual | 924 | 970 | 895
Originated Loans [Member] | Commercial Loans [Member] |  |  |
Financing Receivable, Impaired [Line Items] |  |  |
Average recorded investment | 8,183 | 14,498 | 12,493
Interest income recognized accrual | 171 | 221 | 302
Originated Loans [Member] | Commercial Loans [Member] | Commercial [Member] |  |  |
Financing Receivable, Impaired [Line Items] |  |  |
Average recorded investment | 1,841 | 6,217 | 2,219
Interest income recognized accrual | 0 | 0 | 71
Originated Loans [Member] | Commercial Loans [Member] | Commercial Real Estate [Member] |  |  |
Financing Receivable, Impaired [Line Items] |  |  |
Average recorded investment | 3,534 | 5,828 | 8,538
Interest income recognized accrual | 115 | 167 | 164
Originated Loans [Member] | Commercial Loans [Member] | Agricultural [Member] |  |  |
Financing Receivable, Impaired [Line Items] |  |  |
Average recorded investment | 224 | 715 | 148
Interest income recognized accrual | 1 | 1 | 1
Originated Loans [Member] | Commercial Loans [Member] | Agricultural Real Estate [Member] |  |  |
Financing Receivable, Impaired [Line Items] |  |  |
Average recorded investment | 1,709 | 908 | 628
Interest income recognized accrual | 43 | 44 | 45
Originated Loans [Member] | Commercial Loans [Member] | Business Banking [Member] |  |  |
Financing Receivable, Impaired [Line Items] |  |  |
Average recorded investment | 875 | 830 | 960
Interest income recognized accrual | 12 | 9 | 21
Originated Loans [Member] | Consumer Loans [Member] |  |  |
Financing Receivable, Impaired [Line Items] |  |  |
Average recorded investment | 8,439 | 8,286 | 7,070
Interest income recognized accrual | 457 | 480 | 374
Originated Loans [Member] | Consumer Loans [Member] | Indirect [Member] |  |  |
Financing Receivable, Impaired [Line Items] |  |  |
Average recorded investment | 35 | 8 | 0
Interest income recognized accrual | 3 | 0 | 0
Originated Loans [Member] | Consumer Loans [Member] | Home Equity [Member] |  |  |
Financing Receivable, Impaired [Line Items] |  |  |
Average recorded investment | 8,226 | 8,278 | 7,070
Interest income recognized accrual | 446 | 480 | 374
Originated Loans [Member] | Consumer Loans [Member] | Direct [Member] |  |  |
Financing Receivable, Impaired [Line Items] |  |  |
Average recorded investment | 178 | 0 | 0
Interest income recognized accrual | 8 | 0 | 0
Originated Loans [Member] | Residential Real Estate Mortgages [Member] |  |  |
Financing Receivable, Impaired [Line Items] |  |  |
Average recorded investment | 6,523 | 6,143 | 5,128
Interest income recognized accrual | 296 | 269 | 219
Acquired Loans [Member] |  |  |
Financing Receivable, Impaired [Line Items] |  |  |
Average recorded investment | 93 | 1,205 | 7,779
Interest income recognized accrual | 0 | 0 | 0
Acquired Loans [Member] | Commercial Loans [Member] |  |  |
Financing Receivable, Impaired [Line Items] |  |  |
Average recorded investment | 93 | 1,205 | 7,779
Interest income recognized accrual | 0 | 0 | 0
Acquired Loans [Member] | Commercial Loans [Member] | Commercial [Member] |  |  |
Financing Receivable, Impaired [Line Items] |  |  |
Average recorded investment | 0 | 0 | 2,045
Interest income recognized accrual | 0 | 0 | 0
Acquired Loans [Member] | Commercial Loans [Member] | Commercial Real Estate [Member] |  |  |
Financing Receivable, Impaired [Line Items] |  |  |
Average recorded investment | 93 | 1,205 | 5,734
Interest income recognized accrual | $ 0 | $ 0 | $ 0

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- Definition Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5212-111524 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5258-111524 + Details
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